Modern Hydronics February 2014

MODERN HYDRONICS 2014 FEBRUARY

Teaming Up With AIR-TO-WATER HEAT PUMPS

The Lure of

HYBRID SYSTEMS STEP-BY-STEP RADIANT COOLING RESIDENTIAL INFLOOR: INSTALLATION METHODS SNOW AND ICE MELT BASICS A PUBLICATION OF

HOW TO USE PUMP TROUBLESHOOTING TOOL PRODUCT SHOWCASE

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CONTENTS

a supplement of Heating Plumbing Air Conditioning Magazine HPAC MAGAZINE 80 Valleybrook Drive, Toronto, ON M3B 2S9 TEL: 416.442.5600 FAX: 416.510.5140 www.hpacmag.com EDITOR Kerry Turner (416) 510-5218 KTurner@hpacmag.com ASSISTANT EDITOR

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MH4

COMBI-SYSTEMS

MH8

COOLING

Heat Pump Plus Part I By John Siegenthaler Why and how to do radiant cooling By Robert Bean

MH12 SNOW AND ICE MELT

Embedded systems: a radiant concept By Mike Miller

MH14 PUMPS

Troubleshooting pump performance By Larry Konopacz

MH16 INFLOOR HEATING

The path to near net-zero is underfoot By Steve Rohrbaugh

MH20 HYDRONIC PRODUCT SHOWCASE

MH26 COMBI-SYSTEMS

Heat Pump Plus Part II By John Siegenthaler

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FEBRUARY 2014

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>> Combi-systems

Heat Pump Plus How to combine an air-to-water heat pump with a boiler (Part I).

A

ir-to-water heat pumps (AWHPs) represent a growing alternative to geothermal heat pumps in many parts of North America. While arguably not suited for consistently bitter cold climates, they can hold their own in moderate Canadian climates such as the southern parts of British Columbia and southern Ontario.

An AWHP gathers low temperature heat by refrigerating outdoor air during the heating season. The low-grade heat Figure 1 Heating Performance

INSIDE

OUTSIDE

AIR-TO-WATER! HEAT PUMP

leaving load water temp = 86 ºF

leaving load water temp = 104 ºF

leaving load water temp = 122 ºF 80000

Heating capacity (Btu/hr)

70000 60000

AIM LOW

is “upgraded” to higher temperature heat using a standard refrigeration cycle.

This heat is transferred to a stream of water, (or water/antifreeze) mixture, where it is ready for distribution using a low temperature hydronic distribution system.

In areas where low-priced natural gas is not available, the cost of heat delivered by an AWHP, on a $/MMBtu delivered basis, is often significantly lower than that delivered by propane or fuel oil. Since most AWHPs operate on electricity, they can also be combined with on-site electrical generation such as provided by solar photovoltaic systems. This option is especially attractive where net metering is available.

Another compelling reason to use an AWHP is that it can provide cooling during warm weather. Just like most geothermal and air-to-air heat pumps, AWHPs contain refrigerant reversing valves that let them serve as chillers. As such they can produce a steady stream of chilled water in the temperature range of 45 to 60F for use in hydronic cooling systems.

The heating performance of an AWHP depends on outdoor temperature, as well as the load water temperature. The warmer it is outside and the lower the leaving load water temperature (the temperature of water leaving the heat pump condenser), the higher the heating capacity and coefficient of performance (COP), as shown in Figure 1.

There is not much anyone can do to alter outdoor air temperature, however, designers do have options when it comes to determining the load water temperature required of the heat pump.

The goal is simple: design the heating distribution system for the lowest possible supply water temperature.

My suggestion is to design all hydronic distribution systems, especially those that will be (or might be) connected to heat pumps, so that they will deliver full design load output with a supply water temperature not exceeding 120F. Systems using low temperature floor, wall and ceiling radiant panels, as well as generously sized panel radiators, can all meet this criteria. In some cases, even

Figure 2 Simple Method of Operation

50000 40000

0

10 20 30 40 50 60 Outdoor air temperature (ºF)

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leaving load water temp = 86 ºF

leaving load water temp = 104 ºF leaving load water temp = 122 ºF 6.5 6 5.5 5 COP

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heating load "duration curve"

heat supplied by auxiliary boiler balance point

2.5 0

10 20 30 40 50 60 Outdoor air temperature (ºF)

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spare heating! capacity of heat pump

50%! design! load

heat supplied by heat pump

no! heating! load

3 2 -10

space heating load (Btu/hr)

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heating capacity of heat pump

design! heating! load

hours 1000

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5000

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BOOST AND BACKUP In cold climates there are times when the heating capacity of an AWHP will likely fall short of the heating load. This can occur when the outdoor temperatures are at, or close to, their minimums.

It can also occur during periods of high demand, such as during recovery from temperature setbacks. At these times, a supplemental heat source can provide the extra heat needed.

If propane is available and cost competitive against straight electric resistance heating on a $/MMBtu delivered basis, a modern propane-fueled mod/ con boiler is a good choice as the supplemental heat source. Having such a boiler also provides a “backup” heat source if the heat pump is out of service.

The relatively low electrical wattage required also allows it to operate from modestly-sized standby generators during power outages.

There are two ways to use the auxiliary boiler to supplement a heat pump. The first uses either the AWHP, or the boiler, as the system’s sole heat source, depending on outdoor temperature. The second allows the possibility of using both heat

sources simultaneously. Which approach is best depends on the relative cost of energy supplied by the heat pump versus the fuel used by the boiler. It also depends on how low the outdoor temperature can drop before the heat pump should not be operated. Many modern AWHPs can operate at outdoor temperatures as low as -4F, albeit at significantly reduced heating output and low COPs.

EITHER/OR The first method of operation is simple.

Use the heat pump to supply the heating load until the outdoor temperature drops to the point where the heat output from the heat pump is insufficient to meet the load. Then, turn off the heat pump and turn on the boiler. This concept is illustrated in Figure 2.

The heating load duration curve represents the severity of the heating load versus the number of hours that the load is equal to or above a given percentage of design load. For example, in Figure 2, the heating load is equal to or above 50 per cent of a design load of about 1900 hours per year, as shown by the yellow lines. This graph also assumes that an average heating season lasts 5000 hours per year, which is just under seven months. continued on pMH6

Figure 3 Continuous Heat Pump Operation

space heating load (Btu/hr)

design! heating! load

no! heating! load

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heating capacity of heat pump heating load "duration curve"

heat supplied by auxiliary boiler balance point

spare heating! capacity of heat pump

heat supplied by heat pump during of heating season (hours)

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>> Combi-systems continued from pMH5 The exact shape of the heating load duration curve varies from one climate location to another. However, the curve’s general shape will remain similar to that shown in Figure 2.

This curve shows that the number of hours of severely cold weather, when the heating load is perhaps 90 per cent or more of design load, are very limited, compared to the hours where the heating load is a smaller percentage of design load.

The “balance point” is where the heat output from the heat pump equals the heating load. The red shaded area to the left of the balance point represents the time during which the boiler is meeting the load. In Figure 2, this is approximately 600 hours per heating season. The blue shaded area represents the time when the heat pump supplies the heating load.

In Figure 2 this is about 4400 hours per year (i.e., all but the time the boiler is supplying the load).

The mathematical areas under the heating duration curve represent the total energy supplied. The red area represents the total energy supplied by the boiler and the blue area shows the total energy supplied by the heat pump. Assuming that energy supplied by the heat pump is less expensive than that supplied by the boiler, the goal is to minimize the red area as a percentage of the total area under the curve. The extent to which this can be done depends on the heating capacity of the

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AWHP relative to the design load. It also depends on how the heating capacity of the heat pump “falls off” with decreasing outdoor temperature. Selecting a higher capacity AWHP, relative to the design load, will move the balance point to the left, decreasing the energy contribution of the boiler. However, it will also increase installed system cost. In general, the more expensive the boiler’s fuel is compared to the heat supplied by the heat pump, on a $/MMBtu basis, the farther the balance point should be moved to the left. This minimizes the energy contribution of the more expensive boiler fuel.

The pink shaded area shows where the heat pump’s heating capacity exceeds the load. This area implies that “spare” heating capacity is available from the AWHP much of the heating season. Good designers will use this available capacity for preheating, or perhaps even fully heating domestic water.

The second approach to combining an AWHP with a boiler keeps the heat pump in operation whenever there is a heating load and supplements its output, as necessary, using the boiler.

This scenario is represented in Figure 3.

Notice how the blue shaded area now spans the entire heating season. The red shaded area is significantly smaller than in Figure 2, indicating that the boiler supplies a smaller percentage of the total space heating required over the season.

The feasibility of this approach depends on several factors.

First, can the heat pump operate during the coldest outdoor air temperatures experienced at the site? In some parts of Canada the answer is likely yes. In bitter cold areas with outdoor temperatures dropping below -5F (-20C) the answer is likely no. The heat pump manufacturer should be consulted for information on the minimum acceptable outdoor temperature at which the unit should be operated.

Second, how does the cost of heat supplied by the heat pump, operating under low outdoor air temperatures, compare to that supplied by the boiler, on a $/MM basis. Remember that the COP of the AWHP under very low outdoor temperatures may be in the range of 2.0, or perhaps even less. If the cost of energy supplied by the boiler is comparable to that supplied by the heat pump, there may not be any incentive to keep the heat pump operating under very low outdoor temperatures. Shut it off and save the operating hours for more favourable conditions.

Part II of this article (see page MH26) shows and describes a specific system combining an AWHP and mod/con boiler. <> - JOHN SIEGENTHALER

2 Gal. (7.6L)

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John Siegenthaler, P.E., is a mechanical engineering graduate of Rensselaer Polytechnic Institute and a licensed professional engineer.

He has over 34 years experience in designing modern hydronic heating systems. He is also an associate professor emeritus of engineering technology at Mohawk Valley Community College in Utica, NY. MODERN HYDRONICS

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>> Cooling

Why And How To Do Radiant Cooling "Have you ever considered that most naysayers of hybrid radiant-based HVAC systems say the problem is that you need two systems, one for comfort and one for ventilation; and yet many ventilation experts agree that independent ventilation systems are preferred – go figure."

W

hen it comes to radiant there is no shortage of myths, we address at least 45 of them at www. healthyheating.com. One undisputable whole truth about radiant is its role as an “enabler,” specifically when we talk about the hybrid radiant cooling system. It enables the preferred separation of thermal comfort from ventilation. Translation: it facilitates the use of 100 per cent dedicated, ducted and distributed outdoor air (DOAS). This system has many advantages in that its sole existence is for the exclusive tasks of dehumidification, deodorization and decontamination.

In comparison to all-air systems, the air part of a hybrid is designed and assembled around significantly reduced air flows leading to smaller air handlers, filters, ducts, dampers and fabrication and installation accessories. All of the above translates to a more effective system for less capital cost and lower operating and maintenance costs. Additionally, these dedicated duty systems are very effective at regulating the environmental conditions necessary for controlling microbial population, hydrolysis, swelling in hygroscopic materials, and in promoting respiratory and thermal comfort.

From an energy and exergy efficiency perspective, the sensible part of the hybrid radiant cooling systems is associated with tepid fluid temperatures in the range of 55F to 70F (13C to 21C) for high performance buildings using masonry type flooring. This makes them ideal for direct ground coupled exchangers, evaporative cooling with or without night sky radiation, and promote the possibility of compressorless cooling systems; or at the very least the ability to bypass the compressor for all but peak loads. The high return temperature range of 60F to 75F (16C to 24C) also maximizes efficiency from cooling plants and reduces transmission gains.

Radiant systems also serve the needs of architects and interior designers through greater freedoms with space, the ability to use low VOC materials and superior capacity in handling direct solar load with a quieter and more pleasant solution.

DESIGN CONSIDERATIONS As much as industry might want there to be a Radiant Cooling for Dummies – there is not. In fact, I would be disturbed to think that such a book would be published. We have enough MH8 | FEBRUARY 2014

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stupid radiant heating tricks out there. We do not need to pile on radiant cooling fiascos. The designer and contractor must understand the interactions and connections between buildings, the indoor environment and HVAC systems and controls.

It is not difficult but it does require skill sets beyond the typical hydronics only or air only technician. It requires a hybrid radiant-based HVAC designer and contractor.

ABRIDGED HOW IT IS DONE First, understand that the objective in the hybrid design is to introduce dedicated lean ventilation air to the space reflecting the anticipated latent loads from occupants, infiltration and other sources. The dry supply air will act as a sponge to maintain space operating conditions below the dew point of the radiant panel.

Panel surface and radiant asymmetry temperature limits will be within the range established by ANSI/ASHRAE 55 - Thermal Environmental Conditions for Human Occupancy.

Let’s look at a simplified example of a small 30' x 30' x 10' classroom with a maximum occupancy of 30 people and a space sensible cooling load (qs) calculated to be 28 584 Btuh (8.4kW) and space conditions maintained at 74F (23.3C) operative temperature (top ) and 50 per cent relative humidity (rh). From the psychrometric chart, this gives a dew point temperature of ≈ 54F (12.2C) and a moisture content of ≈ 0.00896 lbH2O/lbdry .

1. Using a 100 per cent outdoor air supply per person of 20 cfmiii, ventilation flow rate (Qv) becomes (all calcs in IP units): Qv = 30 persons•20 cfm pp = 600 cfm [1] 2. The latent load (qL) due to occupants is calculated, using an estimate of 200 to 220 Btuh/per person (approximation from ASHRAE activity tables ) as: qL = 30 occupants x 220 Btuh/pp = 6600 Btuh [2] 3. The humidity ratio differential (Δω) due to ventilation is calculated for the occupant latent load as: qL = latent heat of vaporization (Lv )•air flow rate (Q)•Δ in humidity ratio (Δω) [3] qL = ( 60 min/h•1076 Btu/lb water•0.075 lb air/ft3 )•600 cfm•Δω qL = 4840 Btu-min/ft3-hr•600 cfm•(Δω)

MODERN HYDRONICS

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4. From formula [2] the occupant latent load, qL = 6,600 Btuh, and now Δω can be calculated using [3]; 6600 Btuh = 4840 Btu-min/ft3-hr•600 cfm•(Δω), Rewritten to solve for Δω; Δω = qL/Lv•Q [4] Δω = 6600 Btuh/(4840•600 cfm) Δω ≈ 0.00227 lbH2O/lbdry 0.00227 lbH2O/lbdry represents the humidity ratio differential for 30 people.

5. For determining dew point, calculate the maximum anticipated humidity ratio (ωoccupied) starting with a space operating condition of 74F (23.3C) @ 50 per cent rh adding a 30 person load (infiltration and other possible latent loads ignored for this example): ωoccupied = ωoperating + ωpeople …+ ωother [5] ωoccupied = ω(74°F@50%rh) + ω(30 people @ 220 Btu/pp) ωoccupied = 0.00896 lbH2O/lbdry + 0.00227 lbH2O/lbdry ωoccupied = 0.01123 lbH2O/lbdry From the psychrometric chart (Figure 1), ωoccupied = 74F @ 62.5 per cent rh equals a dew point of 60.4F 6. Establish the minimum allowable surface temperature of the radiant panel (tp); based on good practice, select for ≈ 2F to 3F (1C to 1.5C ) minimum Δt above the dew point : tp = ωoccupied-dp + 3F [6] tp = 60.4F + 3F = 63.4F (17.5C) Notwithstanding radiant asymmetry and comfort, 63.4F (17.5C) represents the lowest allowed panel surface temperature with a sufficient safety margin to prevent surface condensation.

Figure 1 Lean supply air at 55F @ 50 per cent rh delivered to space to control moisture conditions below dew point of radiant panels. Shown is minimum floor surface temperature of 66F (19C) based on ANSI/ASHRAE 55.

7. Calculate sensible supply air capacity (qs): with an operating space dry bulb of 74F (23C) and designer choice supply dry bulb of 55Fv , the sensible air capacity becomes: qs = 60 min/h•(specific heat, Cp)•(density, ρ)•(air flow rate, Q)•Δt [7] qs = (60 min/h•0.244 Btu/lbF•0.075 lb/ft3 )•cfm•Δt qs = 1.08•cfm•Δt qs = 1.08•600•(74F - 55°F) qs = 12 517 Btuh 12 517 Btuh represent the sensible air cooling capacity of the supply air. This value, deducted from the 28 584 Btuh total sensible required, is what the radiant cooling panel must absorb.

8. The sensible cooling load placed on the radiant panel becomes: qs,panels = Total load (sensible) – air cooled (sensible) [8] qs,panels = 28 584 Btuh - 12 517 Btuh qs,panels = 16 069 Btuh This 16 069 Btuh can be assigned to a radiant ceiling, wall or floor or combination of cooling panels if necessary.vii 9. The required radiant panel surface flux (heat absorption) becomes: qflux = qs, panel/Aavailable panel area [9] qflux = 16 069 Btuh/(30 ft x 30 ft) qflux = 17.85 Btuh/ft2 This 17.85 Btuh/ft2 can be absorbed from any type of radiant panel.

10a. For radiant ceiling cooling, the surface temperature (ts) becomes: ts = top – (qflux/heat transfer coefficientviii) [10a] ts = 74F – (17.85 Btuh/ft2 /1.94 Btuh/°F) ts = 64.8F > 63.4F (safety margin temperature) > 60.4F (occupied dew point) = good Since 64.8F (18.2C) is above the safety margin limit of 63.4F (17.4C) and more than the 60.4F (15.8C) occupied dew point this would be an acceptable solution.

10b. For radiant floor cooling, the surface temperature (ts) becomes: ts = top – (qflux / heat transfer coefficientv) [10b] ts = 74F – (17.85 Btuh/ft2/1.23 Btuh/ft2 °F) ts = 59.5F (15.3C) ts= 59.5F < 60.4F (occupied dew point) < 63.4F (safe) & < 66F min.

Since 59.5F (17.5C) is below the occupied dew point of 60.4F (15.8C) and below the acceptable 66F (19C) surface temperature for thermal comfort, this would be an unacceptable solution without modifications to rework design for; higher operative temperature (top) or increase panel surface area (A), add peak cooling panels or second stage cooling coils or improve zone enclosure to get sensible loads down.

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FEBRUARY 2014

| MH9

>> Cooling Figure 2 Overview of the operating characteristics for the hybrid radiant based HVAC system in the cooling mode.

10c. For radiant wall cooling, the surface temperature (ts) becomes: ts = top – (qflux/heat transfer coefficientv) [10c] ts = 74F – (17.85 Btuh/ft2/1.41 Btuh/ft2 °F) ts = 61.3F ts = 61.3F > 60.4F (occupied dew point) < 63.4F (safety margin temperature) Since 61.3F (16.3C) is above the occupied dew point of 60.4F (15.8C) but below the acceptable safety margin surface temperature of 63.4F (17.4C) this is a riskier application and would be an unacceptable solution without modifications to rework the design for; higher operative temperature (top) or increase panel surface area (A), add peak cooling panels or second stage cooling coils or improve zone enclosure to get sensible loads down.

Now that we have determined the sensible load on the panel system and sensible and latent load on the air system, we need to determine the capacity of the cooling coil in the air handler.

12. Sensible (qs), latent (ql) and total load (qt) on coil is calculated using: q = 60 min/h•density (ρ)• air flow rate (Q)•enthalpy differential (Δh) [12] q = (60 min/h•0.075 lb/ft3)•cfm•Δh q = 4.5•cfm•Δh qs = 4.5•600•(h3 – h2) = 2700•(25.45 – 18.17) = 19 656 Btuh ql = 4.5•600•(h1 – h3) = 2700•(43.44 – 25.45) = 48 573 Btuh qt = 4.5•600•(h1 – h2) = 2700•(43.44 – 18.17) = 68 229 Btuh In a nut shell, that is the why and how process for doing a radiant cooling system; albeit a simplified description since it does not describe re-heat or heat recovery potentials of the system. A competent HVAC engineer or technician would be able to describe all the necessary processes for each application and choice in DOAS equipment.

It is sufficient to say that radiant cooling is becoming a big thing, especially for commercial buildings. There is no need to pay attention to the myths nor is there any need to experiment. The applications and calculation procedures are proven and the working projects all over the world are demonstrating the energy and comfort features and benefits realized by radiant-based HVAC systems.ix,x

- ROBERT BEAN Robert Bean, R.E.T., P.L.(Eng.) is president of Indoor Climate Consultants Inc. and a director of www.healthyheating.com.

He serves on ASHRAE Committees: T.C.61. (CM), T.C.6.5 (VM), T.C. 7.04 (VM), SSPC 55 (VM). www.healthyheating.com i Radiant Mythology: myths about low temperature radiant heating and high temperature radiant cooling <http://www.healthyheating.com/Radiant_Mythology/

11. Calculate sensible (qs), latent (ql) and total load (qt) for cooling and dehumidification load for the dedicated outdoor air system to take 600 cfm of 100 per cent outdoor air from an example of 85F (29C) @ 80 per cent rh (h1, ω1) to a supply air of 55F (13C) @ 50 per cent rh (h2, ω2).

State point conditions from the psycrometric chart: h1 = 43.44 Btu/lbdry ω1 = 0.0210 lbH2O/lbdry h2 = 18.17 Btu/lbdry ω2= 0.0046 lbH2O/lbdry h3 = 25.45 Btu/lbdry ρ = 0.0750 lb/ft3

Radiant_Floor_Heating_Myths_.htm#.UrHdYeLDseI> ii Sensible loads: ASHRAE 55, ISO 7730, CSA F280 and Ventilation loads: ASHRAE 62.1, 62.2 and CSA 326 iii The actual cfm/person is determined by a method acceptable to the authority having jurisdiction, sample procedures are defined in ANSI/ASHRAE Standard 62.1, 62.2 and CAN/CSA-F326-M91 (R2010) iv 2009 ASHRAE Fundamentals Handbook, Chpt.18, Section 4 v This is purely based on experience but you can see how changing the target number will have a “flow through” effect on the design. vi The 28 584 Btuh total load came from the heat gain calculation (not described in this example). vii Bean, R. Together Forever (Using the ASHRAE Radiant Design Nomograph), HPAC Canada, March 2012. viii *Heat transfer coefficients (htc) - are empirical values determined from experiments

Where, hn = enthalpy at state point ωn = humidity ratio at state point ρ = air density MH10 | FEBRUARY 2014

(ref.: ASHRAE, REHVA and ISSO) ix Radiant Cooling Design Manual, Embedded Systems for Commercial Applications, Uponor, 2013 x Hydronic Cooling, idronics Journal of Design Innovation for Hydronic Professionals, Caleffi, July 2013 MODERN HYDRONICS

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LET’S APPLY THE

POWER OF e.

Introducing the ecocirc XL and Series 80 ITSC. The latest in a full line of efficient and highperforming Bell & Gossett pumps. Backed by the unmatched applications expertise and systemsdriven approach of Xylem, the Bell & Gossett e series and sensorless Integrated Technologic VFD are designed to improve overall system reliability and support operational and energy savings.

Apply the power of e today. Visit us at booth #413 at the Canadian Mechanical & Plumbing Exposition, March 19-21 in Toronto. Go to power-of-e.com.

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MH2014_8-11_Bean.indd 11

14-02-07 2:01 PM

>> Snow Melting

Embedded Systems: A Radiant Concept

Snow and ice melt basics.

SNOW.

It is part of nature's beauty, especially in Canada. But for commercial and institutional facilities, it is a cumbersome winter guest. Building owners and facility managers are well aware of the importance of proper snow removal for safe and easy access, prevention of slip and fall injuries and protection from potential lawsuits.

The conventional methods of snow removal â&#x20AC;&#x201C; plowing, shoveling, salting and sanding â&#x20AC;&#x201C; can impose a great financial burden every year. The cost is not just for the labour and materials associated with the removal, but also the wear and tear on the surfaces in and around the structure. Traditional snow-removal methods can even be an environmental challenge if chemicals are used that are either tracked into the building by guests or absorbed into the ground during the spring thaw.

BEING IN CONTROL When it comes to controlling the system, there are several options to choose from, such as automatic, semi-automatic, manual and idling.

Fully automatic system: a sensor is placed in the ground to detect when snowfall begins.

The sensor sends a signal to the heat source to activate the warm liquid flow through the radiant tubing. Once the snowfall stops and the sensor is dry and clear from snow and ice, the sensor sends a signal to stop the water flow and shut down the system. This energy-efficient method of controlling a snow melt system is typically the most economical as it runs only when needed.

Semi-automatic control: a manual intervention is required to start the system, but a timer is also included that will operate for a preset amount of time and then shut the system off when it times out. This could cause the system to be started MH12 | FEBRUARY 2014

MH2014_12-13_Miller.indd 12

too late and when the timer stops, the system could shut off too early or too late â&#x20AC;&#x201C; both undesired outcomes.

Manual control: the system turns on and off with the flip of a switch. While this is by far the most cost-effective option to install with a snow-melt system, it generally costs more to operate. The human interface requirement typically does not align with that of perfect timing to start or stop a system when compared to the fully automatic system.

Idling: Another option is to idle the system at a preset temperature, typically 22F to 28F (-5C to -2C), to ensure it can ramp up quickly in the event of snowfall. This option is often useful in critical areas that must remain snow and ice free, such as walkways or entryways to buildings.

The idle option can be used with either automatic or semi-automatic controls.

MODERN HYDRONICS

WWW.HPACMAG.COM

14-02-07 3:31 PM

Modern Hydronics

Hydronic snow melting has been gaining traction on commercial and residential properties in recent years. It has been found to help reduce both annual maintenance costs and environmental concerns.

Just like a radiant floor heating application, these systems circulate a warm water/glycol mixture through crosslinked polyethylene (PEX) tubing embedded in the ground. This is the same PEX tubing you use in a radiant floor heating system to heat a residential or commercial structure. The technology has been proven effective for more than 40 years in North America and even longer in Europe.

Embedded hydronic snow melting systems can be effectively used in any exterior area, including stairs, sidewalks, driveways, parking lots and ramps, loading docks, building entrances, wheelchair access ramps, hospital emergency entrances, and helipads on building tops. Almost any area that accumulates snow or ice can benefit from a snow-melting system.

- MIKE MILLER Mike Miller is director of business development, Canada, with Uponor Canada Ltd. and vice chair of the Canadian Hydronics Council (CHC). He can be reached at mike.miller@uponor.com.

DESIGN AND INSTALLATION CONCEPTS Designing an effective snow-melting system requires consideration of several factors, including Btu/sq.ft./hour load requirements, snowfall rates, snow density, snow temperature, outside temperature, wind speed, tubing size, and tubing spacing. All these factors help the designer and installer create a system that will be the most efficient and effective for the project at hand. As the installer you will need to consider a number of options: Installation method: There are several different methods for installing the PEX tubing, including tie-downs to wire mesh or rebar, or stapling to rigid foam.

Tubing type: When choosing the type of PEX to use it is important to use tubing that includes an oxygen barrier. This is because oxygen can migrate through PEX walls that do not have a barrier and corrode the ferrous components such as the boiler and pumps, in a hydronic radiant system.

It is possible to use a PEX product without an oxygen barrier in a hydronic radiant application, but the system design must ensure that there are no ferrous components, or that such components are isolated from the tubing to prevent corrosion and damage.

Heat source: The heat source for snow-melting systems can vary from traditional modulating-condensing boilers to solar, geothermal and even waste heat.

SCHOOLYARD LESSON In terms of control human intervention is not always a good thing as was discovered at a school with a snow melt system in its playground. The system has basically the same setup as a commercial sidewalk or residential driveway snow melt system, but with a slight variation. A layer of soft material was applied on the concrete substrate to cushion the play area. The fully automatic system employed a sensor to detect falling snow and activate the boiler, which activated the system (as described above).

When the system was first installed, a school official turned the system off during the winter break. It snowed quite a bit during that time and with the system off, the snow accumulated and had to be shoveled off.

ď&#x201A;&#x201E;

Lesson: Let the system function as it is designed to.

Fully automatic systems need to be turned on for the entire season if the user is to reap the benefits.

WWW.HPACMAG.COM

MH2014_12-13_Miller.indd 13

MODERN HYDRONICS

FEBRUARY 2014

| MH13

14-02-07 3:31 PM

>> Circulators

Troubleshooting Pump Performance Understanding information provided on pump curves by the manufacturer and taking some simple gauge readings are a great help for analyzing pumped system problems.

A

manufacturer’s pump performance curves contain data that can help HVAC technicians analyze a pumping installation. Pump curves help identify the system’s operating point, find reasons for a system not performing, and even determine a pump’s impeller diameter.

After designing a pump, the manufacturer usually produces a number of units for performance testing. The tests are necessary to establish how the pump will actually perform. The data collected often includes water flow operating against various system resistances, brake horsepower required, efficiency, and the net positive suction head required for proper operation for the various diameter impellers allowable in the pump volute.

This data is analyzed and then plotted and published as the pump operating characteristics. The pump curve shows how the pump will perform with varying head or flow requirements (see Figure 1).

It is not unusual for a pump’s nameplate to be missing because the information is so important (it usually includes manufacturer’s name, pump model, size, impeller diameter, head and flow for the duty point), that it is often removed for safekeeping.

Unfortunately, at times it is so well safeguarded that it cannot be retrieved. Or, perhaps it is just painted over. Either way, the information on it is not available.

To identify the pump and reestablish the nameplate data, the manufacturer must be determined. Most pumps are made of castings and have casting part numbers and markings on them that identify the pump manufacturer. Once the pump manufacturer is known, the type or model and size can be determined with the help of published literature or a telephone call.

Since larger pumps generally have a family of impeller sizes which can be used with a given pump body, at this point the impeller diameter is unknown. A simple procedure using a pressure gauge and the pump’s curves will identify the impeller size in the pump.

IDENTIFYING IMPELLER SIZE Close the pump discharge valve and take the suction and discharge pressures. This is the “dead-head” condition. Reopen the discharge valve and reset it to the position it was in prior to closing, if it was used to balance the flow. The algebraic difference between the discharge pressure and the suction pressure is the pressure head being generated by the pump. Convert this to feet of water head and determine the correct impeller diameter from the no flow point on the pump curve.

As an example: P discharge = 20.5 psi P suction = 4 in. of Hg vacuum (a negative pressure), but the curves are dimensioned “Head, MH14 | FEBRUARY 2014

MH2014_14-15_pumps.indd 14

Figure 1 The pump curve shows how the pump will perform with varying head or flow requirements.

feet of water.” Therefore, the gauge pressures must be converted.

To convert pressure in psi to head in feet of water, multiply psi by 2.31 and divide by the specific gravity of the fluid being pumped. The specific gravity of water is 1. One inch of Hg is equal to 0.491 psi. Therefore: P discharge = 20.5 psi x 2.31 ft. of water per psi /1 = 47.4 ft. of water P suction = 4 in. Hg x 0.491 psi per in.

Hg = -1.96 psi x 2.31 ft. of water per psi/1 = -4.5 ft. of water Pump head = P discharge P suction = 47.4 -(-4.5) ft. of water Algebraically subtracting a minus is a plus, so: Pump head = 47.4 + 4.5 ft. of water = 51.9 ft. of water Locating this head, 52 ft., at 0 gpm flow on the pump curve in Figure 1, shows the pump impeller diameter to be seven inches.

The system operating point can also be determined by using gauge readings. Take the suction and discharge pressures while the system is operating with the discharge valve in the normal open position. Again, convert these into feet of water and subtract (algebraically) the suction pressure from the discharge pressure. This is the head of the pump at the operating flow.

Follow the head line from the zero flow axis out to where it intersects the previously identified impeller characteristic curve. The flow at that point is the system’s operating flow.

For example: after determining the pump’s impeller diameter to be seven inches, gauge readings of the pump taken while it operated were: P discharge = 17.5 psi P suction = 4 in. Hg (vacuum) Convert the gauge readings for the fluid being pumped to feet of water: P discharge = 17.5 psi x 2.31/1 = 40.5 ft. of water

MODERN HYDRONICS

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14-02-07 2:05 PM

Modern Hydronics

suction = 4 in. Hg x 0.491 psi per in P Hg = -1.96 psi x 2.31 ft. of water per psi/1 = -4.5 ft. of water Pump head = 40.5 - (-4.5) ft. of water = 45.0 ft. of water The pump head of 45 ft. intersects the seven-inch diameter characteristic curve at 55 gpm, which then is the system operating flow. Being able to fully identify a pump, determine the installed impeller size and the system operating point are of key to troubleshooting (see sidebar In The Field).

IN THE FIELD

A two hp base-mounted pump trips its circuit breaker regularly when pumping water. The nameplate specifies an 8 ½ in. diameter impeller with a duty point of 51 gpm at 74 ft. of head. Gauge readings at shutoff are 12 psi suction pressure and 46 psi discharge pressure. When the three-way valve is fully open to the coil, the suction pressure is still 12 psi and the discharge pressure is 44 psi.

When the three-way valve is fully open to the bypass, the suction pressure is still 12 psi, but the discharge pressure is 40 psi.

What is the problem? What is the solution? The first step to solving the problem is to analyze the pump readings.

Shutoff head is (discharge pressure minus suction pressure) x 2.31 = (46 psi - 12 psi) x 2.31 = 78.5 ft. of water The 78.5 ft. at shutoff and the pump curve (Figure 1) confirms the impeller diameter as 8 ½ in.

With the three-way valve fully open to the coil: Pump head = (44 psi - 12 psi) x 2.31 = 74 ft. of water The intersection of 74 ft. of head and the 8 ½ in. impeller curve on Figure 1 indicates a flow of 51 gpm. The horsepower required is 1 ¾. With the threeway valve open to the bypass, the pump head is calculated as follows: Pump head = (40 psi - 12 psi) x 2.31 = 64.7 ft. of water.

The intersection of 64.7 ft. of head and the 8 ½ in. impeller curve on Figure 1 indicates a flow of 80 gpm. The horse-power required is 2 ⅓. The problem is too much flow because the resistance to flow in the bypass circuit is too low.

The solution: increase the resistance in the bypass circuit by 9.3 ft. of water (74-64.7) so the resistance through the bypass circuit is the same as the resistance through the coil. The flow and the horsepower will then be reduced to the same as that flowing through the coil, eliminating breaker trips.

Larry Konopacz is manager of training and education for Bell & Gossett Little Red Schoolhouse. He is a LEED AP and a member of ASHRAE, the Hydraulic Institute, ASPE, and the USGBC. This feature is adapted from a Little Red Schoolhouse article. http://bellgossett.com

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MODERN HYDRONICS

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MH2014_14-15_pumps.indd 15

Understanding the information provided on pump curves by the pump manufacturer and taking some simple gauge readings are fundamental to analyzing pumped system problems.

- LARRY KONOPACZ

FEBRUARY 2014

| MH15

1/30/2014 4:50:30 PM

14-02-07 2:05 PM

>> Energy Management

The Path To Near Net-Zero Is Underfoot

H

omes use a significant amount of energy to operate.

Depending upon the location, about 63 per cent of that energy may be consumed by space heating according to Natural Resources Canada. Given the continual escalation of greenhouse gas emissions, status quo is no longer acceptable.

In many jurisdictions there are initiatives exploring high-efficiency homes and even net-zero energy residential construction, which may develop into new requirements over the next decade. A net-zero home produces as much energy as it uses over the course of a year. But most homeowners are not yet prepared to invest in on-site renewable energy systems to reach net-zero. Perhaps, approaching near net-zero should still be the goal for every residential new construction and renovation project. Now is the time to begin getting comfortable with the higher performing technologies that will shape the future of residential buildings.

The path to near net-zero begins with reducing energy consumption. The crucial first step is reducing the need for energy with a well-insulated, tight building envelope, paving the way for the latest HVAC technologies to have maximum effect. Radiant heating brings a lot to the equation and can be done even better than in the past. For example, combining a high-performance radiant system with a geothermal heat pump and advanced mixing controls puts you on track to cut your heating energy usage by more than half. Once you have selected the optimum wall and roof construction along with low U-value windows and doors, a well-designed radiant heating system should be your next priority in your journey to near net-zero.

CONSIDERING RADIANT DESIGN OPTIONS Understanding current radiant heating installation methods and their performance attributes is fundamental to achieving energy savings. There are three practical and proven methods for residential installations. One is for installers to secure PEX pipes with aluminum heat transfer plates to the underside of the subfloor in joist cavities. Another is to pour a thin slab of concrete that covers the PEX pipes, which are fastened to the top of the subfloor. A third is to fasten heat transfer panels to the top of the subfloor, then snap the PEX pipes into these panels. The choice between these installation methods is influenced by the scope of each project.

BELOW-FLOOR PLATES With many renovations, the homeowner may want to keep the existing wood, tile or marble floor. Heat transfer plates make radiant feasible under these conditions. To drive heat into the room, the underlying joist cavity is filled with insulation typically four to five times greater in R-value than the resistance of the flooring above. The minimum amount of insulation is specified in the CSA B214 Installation Code for Hydronic Heating Systems. A downside to heat transfer plate constructions is that optimal space heating comfort is not achieved. First, it is impossible to configure perimeter and occupied pipe spacing layouts. Second, it is difficult to zone rooms because the joists prevent the installation of the most efficient pipe layouts.

These constraints limit system efficiency.

THIN SLAB OVERPOUR An above-the-floor system such as a wet overpour is widely used in new construction. Overpour installations allow for the quick and easy placement of complex piping layouts that optimize the occupants’ thermal comfort. The thin slab also has a sound deadening effect. Installers need to make sure they have considered the extra material and labour costs to reinforce the subfloor and double plate the walls. Other trades should not be allowed to work inside the home while the thin slab is being poured and the floor finishers should not be scheduled for weeks to months later until the slab is cured.

ABOVE-FLOOR PANELS Heat transfer panels are an above-floor alternative that fits tighter construction schedules and requires less coordination.

Panels and pipes install quickly using typical framing tools and complex piping layouts are easy to configure with basic carpentry skills. Finished flooring can be installed the same day after pressure testing the PEX pipes.

Some renovation projects – such as when there is a full tear out of existing floor and wall coverings – are nearly equivalent to new construction. Either above-floor panels or below-floor plates can be installed. In these retrofit projects, it is generally not practical to reinforce the subfloor. An overpour should not be undertaken without the prior approval of an architect.

Radiant heating is not only under your feet. Heat transfer panels can also be installed in walls and ceilings, behind the continued on pMH18

MH16 | FEBRUARY 2014

MH2014_16-19_rohrbaugh.indd 16

MODERN HYDRONICS

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14-02-07 2:06 PM

ď&#x201A;&#x201E;

MH2014_16-19_rohrbaugh.indd 17

14-02-07 2:06 PM

>> >> Category Energy header Management continued from pMH16 continued from pMH5

Figure 1 High-performance radiant heating panels combined with a ground source heat pump (GSHP) can provide more than 30 Btuh per square foot depending on your finished flooring.

with advanced controls for nighttime or unoccupied setback, resulting in less demand on the high-performance radiant panel system which translates to less energy consumed.

Output Btu-hr per square foot for PQ 0.5 2•°F/Btu-hr finished flooring

50 high performance panels

GSHP hea ng water supply to radiant system 40

thin slab panels

30

plates 20 pipe only 10 20

30

40

50

60

Radiant manifold supply temperature in °C for 20°C ambiaent room temperature and 11°C ΔT

gypsum board, as heating surfaces to increase the heat output into the room.

EVALUATING RADIANT PERFORMANCE The different radiant floor installation methods have significant differences in performance. Pipes underneath the subfloor, either with or without plates, are the least efficient radiant systems at transferring heat into the above room. Plate installations require higher water temperatures to heat the room and there are maximum temperature limits that must be adhered to. Floor coverings, underlayments, adhesives and grouts can be damaged by excessive temperatures leading to discoloration, noise, delamination, warping, cracking and deterioration.

More important than protecting the flooring is to ensure the occupants foot comfort and safety by limiting the surface floor temperatures in accordance with CSA B214. Working within these design temperature limits, the designer often will select supplemental heat to achieve the remaining heat requirements. These separate systems increase the installation costs and are less efficient, resulting in higher energy usage.

Overpour and high-performance heat transfer panel installations are more efficient at spreading the heat evenly underneath the flooring, allowing the room to be heated with lower water temperatures. High-performance heat transfer panels, with their low thermal mass and high heat conductivity, result in a quicker response time than overpour radiant systems.

Quicker response, particularly during the spring and fall “shoulder” months, adds efficiency and increases comfort by reducing the tendency to overheat the room, which can occur with slab systems. Also this fast pick-up time can be combined MH18 | FEBRUARY 2014

MH2014_16-19_rohrbaugh.indd 18

MODERN HYDRONICS

PAVING THE WAY FOR GEOTHERMAL High-performance panels may provide up to 50 per cent higher heat output in comparison to thin-slab overpour or traditional panel and plate systems, and more than double the heat output of just pipes installed in the joist cavity. This higher performance results in a lower required heating water temperature at design conditions. As radiant is optimized, there’s a sweet spot in performance levels where radiant and geothermal are perfectly compatible.

Performance matters with space heating system designs.

Energy savings is typically 25 to 50 per cent with geoexchange compared to other HVAC systems, according to the Canadian GeoExchange Coalition. Geothermal exchange systems do not burn combustible fuel to make heat and they provide three to four units of renewable energy for every one unit used to power the system. High-performance radiant heating panels are best suited to maximize this geothermal advantage by heating the room with low water temperatures that fit in the operating range of geothermal heat pumps without requiring supplemental heating systems.

DESIGNING FOR NEAR NET-ZERO A radiant specialist should get involved early in the project when there is a better chance to influence the design selections. It takes careful planning and involvement from the whole team – architects, radiant designers, general contractors and radiant installers – to achieve maximum energy savings. Together, this team can take steps to get nearer to net-zero by reducing the homeowner's energy requirements with: • Well-insulated walls, ceilings, windows and doors • Efficient and comfortable space heating with high-performance radiant heat transfer panels • High coefficient of performance energy sources such as geothermal exchange Why wait until net-zero is a mandate? With additional planning and a focus on maximizing performance, near net-zero construction is within reach today. Let’s get a few steps down the path by gaining experience with higher performing technologies now and preparing ourselves for a convincing dialogue with homeowners and decision makers.

- STEVE ROHRBAUGH Steve Rohrbaugh is an applications engineer in the building technologies, civil engineering and infrastructure divisions of REHAU North America.

WWW.HPACMAG.COM

14-02-07 2:06 PM

The Evolution of High Efficiency Condensing Boilers

Tx

High efficiency stainless steel boiler Models from 46,000 to 151,000 BTU/Hr Available in a combi version Fully modulating with 5:1 turndown Advanced outdoor reset control Venting to 150' 2" venting on all models up to 100'

MH2014_16-19_rohrbaugh.indd 19

14-02-07 2:06 PM

>> Products

Navienâ&#x20AC;&#x2122;s NCB Series combi-boilers are capable of delivering hydronic heat and domestic hot water for large homes, including those in cold climates. Designed for ease of installation, reliable performance and energy cost savings, the combi-boilers are smaller than a traditional floor-standing boiler and water heater. www.wholehousecombi.com

The Runtal NEO by Runtal North America combines the lines of a Runtal panel with a heat exchanger and low voltage fans to provide increased heating capacity in a compact unit. It supplies high outputs when using low temperature heating solutions such as heat pumps, solar thermal systems or condensing boilers. The NEO is available in two heights (17.5 in. and 23.3 in.) and four lengths (31.5 in., 39.4 in., 47.2 in., and 59 in.). www.runtalnorthamerica.com Heat-Timer Corp.â&#x20AC;&#x2122;s Mini-MOD-CNC allows owners to control a boiler system by automatically mixing and matching non-condensing boiler operation and condensing boiler operation to improve efficiency. It also allows for mixed control of modulating and staging boilers as condensing boilers. www.heat-timer.com

tekmar Designer Touchscreen thermostats are designed with one touch access for temperature settings, schedules and more. A backlit screen features a secondary display area that can show the current floor or outdoor temperature, room setting, or relative humidity level depending on the model and application. With two or four wires, installations are quick to wire and can be done as a communicating thermostat or as a standalone piece. www.tekmarcontrols.com

MH20 | FEBRUARY 2014

MH2014_20-25_Products.indd 20

MODERN HYDRONICS

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14-02-07 3:18 PM

MH2014_20-25_Products.indd 21

14-02-07 3:19 PM

>> Products

Xylem’s Bell & Gossett brand ecocirc XL large wet rotor circulator is designed to enhance commercial hydronic systems its superior qualHeatLink’s two-inch stainless steel manifold

ity and dependability. The ecocirc XL features

is designed for increased flow volume. With

modern hydraulics, advanced motor design

a flow volume of up to 50 gpm it delivers ef-

and intelligent controls. HVAC applications

ficiency at the job site, a compact and con-

include industrial, commercial, recreational,

cise appearance, and the capability to handle

institutional and multi-family residential.

a heavier water flow. For large heating/snow

www.bellgossett.com

melt projects or as a distribution header, The Stiebel Eltron Accelera 300 heat pump

installers do not have to solder copper.

water heater compressor and fan consumes

www.heatlink.com

HBX Control Systems Inc. has designed an

1kWh of electricity to generate the heat equiva-

intuitive control offering ease of use and set-

lent of 3 to 5kWh. It has an 80-gallon capacity,

up. The CPU-0550 stand-alone outdoor reset

2.51 energy factor, 2.2 kW power input, and

control accommodates staging, mixing and

1739 kWh/year power consumption as deter-

differential setpoint and pump sequencer ap-

mined by DOE testing.

plications in a flexible condensed package. It

www.stiebel-eltron-usa.com

features boiler run time rotation, up to three on/off boilers or single modulating boiler, multiple pump selections, and a full colour multigraphic display. www.hbxcontrols.com

Viega’s smartphone app lets users access the company’s complete 3000-product catalogue on their handheld devices. The app includes an integrated notepad feature to make product lists that can be e-mailed to colleagues or customers. It is designed for Apple and Android operating systems and is available for free in the App Store or Google Play. www.viega.net Dahl Mini-Ball balancing valves are designed Weil-McLain Canada’s ECO boiler delivers up to

for radiant floor systems. The compact design

92.5 per cent AFUE. Features include a stain-

features a separate shut-off and memory spin-

less steel fire tube heat exchanger, high mass

dle for balancing by loop length. Tamper resis-

water content design for low-flow resistance,

tant, the valves are available for copper, iron,

and a control with LCD to simplify system set-

PEX, PEX-AL-PEX and CPVC pipes.

up and navigation. www.weil-mclain.ca

www.dahlvalve.com

MH22 | FEBRUARY 2014

MH2014_20-25_Products.indd 22

MODERN HYDRONICS

WWW.HPACMAG.COM

14-02-07 3:19 PM

Modern Hydronics

Amvic Inc. has introduced an

Spirotherm’s Spirovent VDR is a dual-pur-

insulating panel for hydronic

pose device that will remove air and dirt

radiant heat floor systems. The

down to the smallest particle. Construc-

Amvic Insulated Radiant PEX

tion of this combined unit allows for the

panel is designed to reduce

removal of entrained air and dirt particles.

time and labour during instal-

Advantages to the installer and end user

lation. The residential panel is

are isolating valves or replacement filters

made using Type II with R-values

to clog and reduce flow, quiet operation,

of R10, R14, and R18; the com-

minimum pressure drop, no bypass, and

mercial panel is manufactured

dirt can be flushed while the system is in

using Type IX with R-values of

full operation. www.spirotherm.com

R15, R17 and R20. The panel nubs form a mushroom shape to lock the PEX in place. The PEX nubs will accept pipe sizes of ⅓ in., ½ in., ⅝ in., and ¾ in. www.amvicsystem.com The Z-one Relay by Caleffi offers single and multi-zone pump switching relays, and multi-zone valve switching.

The relay interfaces with low voltage

Aquatherm Blue Pipe SDR 17.6 is designed for chilled water, geother-

thermostats or any other low voltage

mal and condenser water mains. A faser-composite layer reduces ex-

controllers having a switching action.

pansion by 75 per cent by blending glass fibres with the PP-R, which

It features front bright LED function

reinforces the pipe and also restricts contraction. Delivering about 20

lights and meets UL873 listed by ETL.

per cent higher flow volume than Aquatherm’s SDR 11, the SDR 17.6 is

www.caleffi.us

less expensive and 35 per cent lighter. www.aquatherm.com

PEOPLE. SOLUTIONS. VALUE. Industry leading service.

It’s what we do. With 20,000 parts stocked on the warehouse floor, an in-house training facility to teach your installers the best techniques on the latest systems, and engineering support with deep experience in hydronics—we have what you need. We can even find the manual for you. Because it’s our business to support yours.

Call us at 1-866-594-0767

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MODERN HYDRONICS

Half Page Aquatech Ad Dimensions: 7 x 4.875 MH2014_20-25_Products.indd 23

FEBRUARY 2014

| MH23

2322_AQ February 10, 2012 14-02-07 3:19 PM

>> Products

The fourth panel from Creatherm combines the

Belimo Americas has released the KR

benefits of its first three radiant floor panels into

actuator on the pressure independent

one product. The S20 Contractor Floor Panel is two-

characterized control valve. It is designed

inches in overall thickness. The lower height profile

for motorizing open-close applications to

makes the snap-tight grid suitable for over-pour or

ensure optimal valve design and repro-

retrofit applications where a thicker panel cannot

ducible

always be used. The S20 is 2 ft. x 4 ft. x 2 in. thick

features a manually adjustable angle of

The Rinnai E Series is designed for homes

and features eight radial staggered snap-tight grids

rotation limiting device with a flow rate

with smaller domestic hot water requirements.

for optimal tubing spacing. www.creatherm.com

scale. www.belimo.com

Two models in the E Series use an integrated

control

quality.

The

actuator

single-speed boiler pump and three-way valve that provide domestic priority and supply a home with heat as well as hot water. E Series “combi” models offer maximum Btuh inputs from 75 000 to 110 000. www.rinnai.us

The KN Series of condensing cast iron boilers is available in sizes ranging from 200 to 3000 MBH. KN-Series boilers offer efficiencies of up to 99 per cent in a compact footprint, and feature

the

HeatNet

boiler

management

system to maximize operating efficiency and turndown ratios. HeatNet can network up to 16 boilers and communicate with a building management system. www.knseries.com MH24 | FEBRUARY 2014

MH2014_20-25_Products.indd 24

MODERN HYDRONICS

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14-02-07 3:19 PM

>> Combi-systems

Heat Pump Plus

How to combine an air-to-water heat pump with a boiler (Part II). fer tank. The water temperature in the buffer tank is regulated based on outdoor reset control. This control selection allows the heat pump to operate at lower condenser temperatures during mild weather, increasing both its heating capacity and COP. Figure 2 Electrical Wiring 240 VAC L1 L2

240 VAC

L1

(RH1-1)

heat pump

INSIDE

OUTSIDE

service switch

boiler (R1)

(RH3-1) (P3)

(RH2-2)

DHW circulator

(R1-1) (P5)

HX1 - tank circulator

(RH2-1) (P2) (RC1-1)

cooling secondary circulator

(RC2-1) (P6) (RC1-3)

(AH1)

(RC2-3)

(AH2)

air handler blower #1 air handler blower #2 transformer 120/24 VAC

24 VAC

off

(MSS)

mode selection switch RC RH W

heat zone valve 1

M

G Y thermostat

(T1)

(VA1)

(RC1)

RH

heat zone valve 2

M

G Y thermostat

(T2)

cooling relay 2

(VA1)

(RC2)

cooling zone valve 1

M

(ZVC1)

cooling zone valve 2

heat (P2) exchanger

valve actuator 3

M

(T3)

zone thermostats

(P5)

(P1)

R W thermostat

DHW

antifreeze protected circuit

(ZVC2)

outdoor temperature

(S7) sensor

outdoor temperature sensor

spring-loaded check valve

(HX2)

(DV1)

(S2) (S4)

sensors in well

(P4)

manifold valve actuators

(VA3)

R W

valve actuator 4

M

thermostat

(T4)

zoned radiant ceiling panels

(P3)

(VA4)

Heating zones 5 through 8 are wired identical to zones 3, 4. make up water

expansion tank

sensor

(S5)

R

(RH1)

C R

(SPC1)

outdoor temperature setpoint controller

(ORC)

C

outdoor reset controller

(S1) (S2)

MH2014_26-32_Siggy2.indd 26

MODERN HYDRONICS

heat relay 1

sensors

heat relay 2 (RH2) (RH3)

MH26 | FEBRUARY 2014

cooling relay 1

RC W

M

modulating/condensing boiler

L2

electric tankless water heater

(P4)

(S4) (S3)

T

(RC2-2)

outdoor reset controller

air to water heat pump (HEATING MODE)

distribution circulator

boiler

T

heat

R

cool

(P1)

Figure 1 Piping Schematic thermostatically controlled electric tankless water heater

L1

main switch (MS)

(RC1-2)

(S1)

N

120 VAC

heat cool

I

n Part I on page MH4 we discussed the energy concepts involved in combining an air-to-water heat pump (AWHP) with an auxiliary boiler. In Part II we will put hardware together into a complete combi-system for heating and domestic hot water. Since we have the heat pump, we will also include a couple of zones of chilled water cooling. Figure 1 shows the overall piping schematic.

This system uses a two-stage self-contained air-to-water heat pump. The outdoor unit is connected to a generously-sized brazed plate heat exchanger located within the heated space. An antifreeze solution is used in the circuit between the heat pump and heat exchanger. It provides reliable freeze protection during a prolonged power outage in sub freezing weather. The heat exchanger is sized to transfer the full output of the heat pump using an approach temperature difference of 5F between the incoming heated antifreeze and the heated water leaving the heat exchanger. This minimizes the thermal penalty associated with having a heat exchanger between the heat pump and the remaining portions of the system. The circuit between the heat pump and heat exchanger includes an expansion tank, combination air/dirt separator, pressure relief valve and fill/purging valves.

The heating distribution system is an extensively zoned low temperature radiant panel system. The rate at which some zones require heat is substantially lower than the heat pumpâ&#x20AC;&#x2122;s first stage heating capacity. The buffer tank stabilizes the heat pump against short cycling under single stage operation.

Notice that the heat exchanger (HX1) is piped so the heat pump works with the slightly lower water temperatures in the lower portion of the buffer tank. This helps maximize the heat pumpâ&#x20AC;&#x2122;s heating capacity and coefficient of performance (COP).

When outdoor temperatures are high enough for the heat pump to meet the heating load, it serves as the sole heat source for the buf-

heat relay 3

WWW.HPACMAG.COM

14-02-07 3:20 PM

Modern Hydronics

When the outdoor temperature drops below a preset value, such as 10F, the heat pump is disabled and the boiler serves as the sole heat source for the buffer tank. The boiler is piped to work with the warmer water in the upper portion of the buffer tank. Even here, the water temperatures are low enough to allow the boiler to operate in condensing mode and thus at high efficiency. Stratification keeps the warmest water in the upper portion of the tank where it can be drawn off for either space heating or domestic water heating. The thermal mass of the buffer tank also protects the mod/con boiler from short cycling.

Domestic water is preheated by the external stainless steel heat exchanger labelled as (HX2) in Figure 1. Whenever the demand for hot water reaches 0.6 gallons per minute (gpm) or more, a flow switch inside the electric tankless water heater closes. This switch closure initiates two simultaneous actions.

First, it turns on circulator (P5) using an isolation relay. This circulator moves water from the upper portion of the buffer tank through the primary side of heat exchanger (HX2), while cold domestic water passes through the other side of the heat exchanger in a counter flow direction.

Second, if the temperature of the domestic water leaving heat exchanger (HX2) is too low for use at the fixtures, the thermostatically controlled tankless water heater elements boost the water temperature as necessary to achieve the required hot water delivery temperature. For more information about “on-demand” subassembly read Only As Needed in HPAC's May/June 2013 issue (the article is also available online at www.hpacmag.com).

ROLE REVERSAL In cooling mode, the heat pump produces chilled water, which is routed to the air handlers. These air handlers have been sized so that their total cooling capacity at a supply water temperature of 50-55F, closely matches the cooling capacity of the heat pump.

The heat pump operates on stage one cooling when one of the air handlers is running. If the second air handler turns on, the heat pump’s internal controller may turn on stage two to maintain adequately low chilled water temperature. Because the cooling capacity of the heat pump and air handlers is reasonably well matched, there is no need to involve the buffer tank during cooling mode operation.

An on/off zone valve regulates flow to each air handler. An ECMbased pressure regulated circulator varies its speed as necessary to provide proportional differential pressure control in the chilled water cooling distribution subsystem. Each air handler contains a drip pan that is connected to condensate drainage piping.

LADDER LOGIC The electrical wiring diagram for this system is shown as a ladder diagram in Figure 2. continued on pMH28 WWW.HPACMAG.COM

MH2014_26-32_Siggy2.indd 27

MODERN HYDRONICS

FEBRUARY 2014

| MH27

14-02-07 3:20 PM

>> Combi-systems continued from pMH27

STEP BY STEP The text that follows is a description of operation of the system.

It is a detailed narration that describes each sequence, beginning with a call for heating or cooling, and ending with that call being satisfied. As you read the description, be sure to cross reference the components mentioned in both the piping schematic in Figure 1 and the electrical diagram in Figure 2. This is where the rubber meets the road when it comes to understanding the details of how this system operates.

1. Space heating mode: The mode selection switch (MSS) must be set for heating. This supplies 24 VAC to the (RH) terminals of thermostats (T1) and (T2).

It also supplies 24 VAC to the (R) terminals of the heating only thermostats shown (T3,T4, etc.). If a thermostat is set for heating mode and it calls for heat, 24 VAC is switched to the thermostat’s (W) terminal. This supplies 24VAC to the associated heating valve MH28 | FEBRUARY 2014

MH2014_26-32_Siggy2.indd 28

Figure 3 R elationship Between Water Temperature and Outdoor Temperature design load condition

110

heat pump is off

105

supply water temperature (ºF)

At first glance, this diagram may look intimidating, But once you get oriented to how a ladder works, it is really straight forward.

The line voltage section at the top of ladder supplies driven loads such as circulators, air handler blowers, and the boiler. Each load is enabled by the closure of a normal open relay contact.

A transformer that reduces 120 VAC line voltage to 24 VAC separates the upper portion of the ladder from the lower portion. The thermostats and other low voltage components are located in the lower portion of the ladder.

The master selection switch located just below the transformer allows the system to operate in either heating or cooling mode, or be switched off.

Two of the thermostats (T1 and T2) control both heating and cooling. The remaining thermostats are heating only devices. To reduce the size of the drawing, only two of the heating only thermostats are shown. The wiring for the other heating only thermostats would be identical to that for thermostats (T3 and T4).

A basic outdoor reset controller turns the heat pump on and off as necessary to regulate the water temperature in the buffer tank. That water temperature depends on the outdoor temperature, as shown in Figure 3.

The warmer it is outside, the lower the water temperature is in the buffer tank. For example, if the outdoor temperature is 20F, the target water temperature is 95F, but if the outdoor temperature is 40F, the target temperature in the buffer tank is only 85F. The outdoor reset controller operates with a differential. In the situation depicted in Figure 3, the differential is set to 5F. Thus, at an outdoor temperature of 40F, the heat pump turns on when the buffer tank temperature (at the sensor location) drops to 85-5/2 = 82.5F, and turns off the heat pump when the sensor temperature reaches 85+5/2=87.5F. Most outdoor reset controllers allow this differential to be adjusted. Wider differentials provide less cycling of the heat source, but also allow greater variation in the water temperature supplied to the load.

reset line

100 95

5ºF differential

90

contacts on reset control!

OPEN to turn off heat pump

85

calculated target temperature contacts on reset control!

CLOSE to turn on heat pump

80 heat pump is on

75 70

70

60

50 40 30 20 10 0 Outdoor temperature (ºF)

-10

no load condition

actuator (VA). When the end switch in that valve actuator closes, 24 VAC is also sent to the coil of relay (RH1). One set of normally open contacts (RH1-1) closes to energize circulator (P4), which then operates in proportional differential temperature control mode.

Upon a call for heating from any thermostat, 24 VAC is also supplied to the outdoor temperature setpoint controller (SPC1), and the outdoor reset controller (ORC). If the outdoor temperature is above the minimum value set on (SPC1) the heat pump will be the heat source. In this case, 24 VAC passes through the normally closed contact within (SPC1) and on to the normally open contact in the outdoor reset controller (ORC). The (ORC) measures the outdoor temperature using sensor (S1) and calculates the target temperature for the buffer tank. It measure the temperature in the upper portion of the buffer using sensor (S2). If the buffer tank temperature is too low to supply the load, the normally open contact in the (ORC) closes. This energizes relay coil (RH2). One normally open contact (RH2-1) closes to energize circulator (P2). Another normally open contact (RH2-2) closes to enable the heat pump to operate in heating mode. The heat pump then turns on circulator (P1) and operates under it own internal control logic.

If the outdoor temperature detected by (SPC1) is below the setpoint value, the normally open contact in (SPC1) closes, and the normally open contact opens. This turns off relay (RH2) and disables operation of the heat pump as well as circulator (P2). It also applies 24VAC to the coil of relay (RH3). Normally open contact (RH3-1) closes as a dry contact across the (T T) terminals in the boiler, enabling it to operate. The boiler turns on circulator (P3) and begins operating under its own internal outdoor reset controller settings. It uses these settings, in combination with the outdoor temperature measure by sensor (S4) to calculate the target temperature in the buffer tank. It measures the temperature in the upper portion of the buffer tank using sensor (S3). When necessary, the boiler fires to raise the temperature of the buffer tank sufficiently high to meet the heating load.

MODERN HYDRONICS

continued on pMH30 WWW.HPACMAG.COM

14-02-07 3:21 PM

B

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MH2014_26-32_Siggy2.indd 29

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14-02-07 3:21 PM

>> Combi-systems continued from pMH28 2. Space cooling mode: The mode selection switch (MSS) must be set for cooling. This supplies 24 VAC to the (RC) terminals of thermostats (T1) and (T2). If either of these thermostats is set for cooling mode, and call for cooling, 24 VAC is switched to the thermostatâ&#x20AC;&#x2122;s (Y) terminal. This supplies 24VAC to the associated cooling relay (RC1) or (RC2). These relays each have 3 sets of normal open contacts.

One set of contacts (RC1-1) or (RC2-1) closes to provide line voltage to cooling circulator (P6), which then operates in proportional differential pressure mode. Another set of contacts (RC1-2) or (RC2-2) closes to provide 24 VAC to the associated cooling zone valves (ZVC1) or (ZVC2). The third set of contacts (RC1-3) or (RC2-3) close to provide line voltage to the associated air handler blowers (AH1) or (AH2). The end switches in the cooling zone valves close when they reach their fully open position.

This signals the heat pump to operate in cooling mode. The heat pump then operates based on its own internal control system.

3. Domestic water heating mode: Whenever there is a demand for domestic hot water of 0.6 gpm or higher, the flow switch inside the tankless electric water heater closes. This closure applies 240 VAC to the coil of relay (R1). The normally open contacts (R1-1) closes to turn on circulator (P5), which circulates heated water from the upper

portion of the buffer tank through the primary side of the domestic water heat exchanger (HX2). The domestic water leaving (HX2) is preheated to a temperature a few degrees less than the current buffer tank temperature. The domestic water leaving (HX2) passes into the thermostatically controlled tankless water heater, which measures its inlet temperature. The electronics within this heater control electrical power flow to the heat elements based on the necessary temperature rise.

All heated water leaving the tankless heater flows into an ASSE 1017 rated mixing valve to ensure a safe delivery temperature to the fixtures. Whenever the demand for domestic hot water drops below 0.4 gpm, circulator (P5) and the tankless electric water heater are turned off.

Keep in mind that this is just one of several ways in which an AWHP and boiler can be combined. That said, this design contains several synergistic details. It leverages a single thermal mass (the buffer tank) to protect both heat sources against short cycling, and stabilize DHW delivery temperature. The buffer tank also provides hydraulic separation between the various circulators that have piping leading to and from the tank. By using outdoor reset control, this design also keeps the supply water temperature as low as possible to maximize performance of both the heat pump and boiler.

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MH30 | FEBRUARY 2014

MH2014_26-32_Siggy2.indd 30

SUPPORT

Versatro

nik

This system does a lot and you may not need all the functionality that it provides. Or maybe you prefer to use other equipment such as a geothermal heat pump or zone circulators rather than zone valves. I will leave it as a challenge to readers to sketch out how this system could be modified for the following: 1. Provide only space heating and domestic water heating.

2. Use small circulators rather than valves for zone flow zoning 3. Use a geothermal water-to-water heat pump rather than the AWHP shown.

All of these modifications are possible. It is just a matter of adding or deleting hardware from the piping and electrical diagrams, and then writing a detailed description of operation for the selected hardware. This flexibility is a testament to what is possible using modern hydronics technology. <> John Siegenthaler, P.E., is a mechanical engineering graduate of Rensselaer Polytechnic Institute and a licensed professional engineer.

He has over 34 years experience in designing modern hydronic heating systems. He is also an associate professor emeritus of engineering technology at Mohawk Valley Community College in Utica, NY. See John at CMPX in Toronto where he is presenting two workshops on March 19 and 20: Unique Hydronic Details For Domestic Water Heating, and Piping and Control Strategies For High Performance Wood-Fired Heating Systems. www.cmpxshow.com/education.cfm MODERN HYDRONICS

WWW.HPACMAG.COM

14-02-07 3:21 PM

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14-02-07 3:21 PM