Mellon Arena Redevelopment | Energy Performance Simulation

Mellon Arena Project MULTIFAMILY C | ENERGY PLUS REPORT

Eleni Katrini (ekatrini@andrew.cmu.edu) Ruchie Kothari (ruchiek@andrew.cmu.edu) Uma Patwardhan (upatward@andrew.cmu.edu)

48722 Building Performance Modeling – Energy Plus

Contents Table of Figures ................................................................................................................................................... 3 [1] Introduction and Methodology ..................................................................................................................... 4 Introduction synthesis .................................................................................................................................... 4 Objectives and Methodology of Simulation.................................................................................................... 5 Building case study description ....................................................................................................................... 6 [2] Design Builder Modeling ................................................................................................................................ 7 Location and Weather Data ............................................................................................................................ 7 Thermal Zones ................................................................................................................................................. 8 Operating Schedules ....................................................................................................................................... 9 Assumptions .................................................................................................................................................. 11 Building Envelope Attributes (Base case)...................................................................................................... 12 Building Envelope Attributes (Proposed case) .............................................................................................. 14 HVAC Systems ............................................................................................................................................... 16 Simulation parameters .................................................................................................................................. 21 [3] Simulations and Results ............................................................................................................................... 23 Comparison A: Case 1 v/s Case 2 .................................................................................................................. 23 Comparison B: Case 2 v/s Case 3 .................................................................................................................. 26 Comparison C: Case 1 v/s Case 4................................................................................................................... 32 [4] Conclusions .................................................................................................................................................. 35 [5] References ................................................................................................................................................... 36

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48722 Building Performance Modeling – Energy Plus

Table of Figures Figure 1 – Master Plan of Urban Development with Location of Multifamily C ................................................. 4 Figure 2 – Methodology for Comparison of all Cases ......................................................................................... 6 Figure 3 : USA map showing Climate zones ........................................................................................................ 7 Figure 4: Floor plans showing thermal zones...................................................................................................... 8 Figure 5 : Retail Weekday.................................................................................................................................... 9 Figure 6 : Residential (Bedroom + Living) Weekday.......................................................................................... 10 Figure 7 : Residential (Living+Kitchen) Weekday .............................................................................................. 10 Figure 8 : Retail Weekend ................................................................................................................................. 11 Figure 9 – Schematic Diagram of HVAC System in Case 1 created by Energy Plus ........................................... 18 Figure 10 – Schematic HVAC diagram created for Case 4 in EnergyPlus .......................................................... 19 Figure 11- Nodal Diagram for Split System with No Fresh Air .......................................................................... 20 Figure 12 – Nodal Diagram for VAV with Reheat System ................................................................................. 20 Figure 13 – Nodal Diagram for Constant Volume DX ........................................................................................ 21 Figure 14 : Annual Energy Use Comparison ...................................................................................................... 24 Figure 15 – Annual Energy End-Use Detail........................................................................................................ 24 Figure 16 : Energy Use Intensity Conditioned Area Comparison ...................................................................... 25 Figure 17 : Energy Use Intensity Total Area Comparison .................................................................................. 25 Figure 18 : Design Loads Comparison ............................................................................................................... 25 Figure 19 : Time Set Point Met During Occupied Hours for Case 1 and Case 2 ................................................ 26 Figure 20 : Time Comfortable Based on Simple ASHRAE 55-2004 .................................................................... 26 Figure 21 – Comparison of Annual Energy Consumption ................................................................................. 27 Figure 22 – Comparison of Energy End Use Consumption - Detail ................................................................... 27 Figure 23 – Energy Use Intensity (EUI) comparison between Case 2 and Case 3 – Conditioned Area ............. 29 Figure 24 – Energy Use Intensity (EUI) comparison between Case 2 and Case 3 – Total Area......................... 29 Figure 25 - Comparison of User Design Loads for Case 2 and Case 3 ............................................................... 30 Figure 26 – Seasonal Energy Comparison for Case 2 and Case 3 ...................................................................... 30 Figure 27 – Time Set Point Met During Occupied Hours for Case 2 and Case 3 ............................................... 31 Figure 28 – Time Comfortable Based on Simple ASHRAE 55-2004 ................................................................... 31 Figure 29 – Comparison of Annual Energy Consumption ................................................................................. 33 Figure 30 – Comparison of Energy End Use Consumption - Detail ................................................................... 33 Figure 31 – Energy Use Intensity (EUI) comparison between Case 1 and Case 4 – Conditioned Area ............. 34 Figure 32 – Energy Use Intensity (EUI) comparison between Case 1 and Case 4 – Total Area......................... 34

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48722 Building Performance Modeling – Energy Plus

[1] Introduction and Methodology Introduction synthesis The project’s objective was the analysis and study of diverse HVAC systems, as well as designing and simulating them on a multifamily building. The building is a part of the urban redevelopment for the Mellon Arena, in Pittsburgh. It is a five-storey building, with both retail and residential uses. Pittsburgh falls under climate zone 5A as per IECC 2012 and has 5986 Heating Degree Days and 654 Cooling Degree Days. This makes it a predominantly cold climate region. For the scope of the study, the building was designed in Design Builder, Version 3.0.0.064, and its HVAC systems were studied both in Design Builder and Energy Plus, Version 6.0. The final simulations were realized in Energy Plus.

In order to study the performance of the building, along with the possibilities that the software has to offer, multifamily C was designed as a baseline and several parametric studies have been conducted. The following parameters were altered in the study: the building envelope (including roof, external walls, glazing, on-grade slab), the input algorithm in glazing type, and the HVAC systems. The scope of these alterations was to understand how the software functions as well as to determine in which cases the building performs better and which HVAC system is the appropriate for this type of building.

N Master plan of Urban development | Multifamily C on the site

Area of redevelopment of Mellon Arena

Figure 1 – Master Plan of Urban Development with Location of Multifamily C

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48722 Building Performance Modeling – Energy Plus

Objectives and Methodology of Simulation This study, due to the complexity of the HVAC systems, had a strong layout and a well-defined methodology.

Initially, the model was created in Design Builder, based on the exterior cell given by the development team [UDA]. Several assumptions were made as far as the interiors are concerned. In the interior layout a series of two apartments were placed with a central corridor for internal movement. Afterwards, materials were assigned to the model based on the prerequisites specified by the UDA. An important part of this assignment was to understand the difference between HVAC systems as well as the difference between alternate inputs in glazing algorithms. Three different HVAC systems were used. For the base case HVAC system, a combination of Split System with No Fresh Air in the residential floors along with a VAV with terminal reheat for the retail floors was applied. For the alternate HVAC system, a Constant Volume DX (unitary multi-zone) for both retail and residential spaces is applied. As far as the type of glazing is concerned, simple input was compared to the more detail spectral one.

After the basic geometric model was set in Design Builder, four separate cases were created from it. The first one was defined by the UDA specified materials, the base HVAC and simple glazing (Case 1), the second one consisted from the UDA specified materials, base HVAC and spectral glazing (Case 2), the third from the UDA specified materials, alternate HVAC and spectral glazing (Case 3) and for the last one new materials, base HVAC and simple glazing (Case 4).

After the four cases were created, based on the methodology, as shown in figure 1, Case 1 and Case 2 were compared in order to understand the difference between the simple and spectral glazing. Afterwards, Case 2 and Case 3 were compared in order to capture the basic differences between the two HVAC systems and evaluate which of the two is more appropriate for type of the building. Finally, the last comparison was between Case 1 and Case 4, hence between base materials and proposed ones.

All the above assessments should be evaluated based on the peak design loads, time set points not met, seasonal energy consumptions and annual energies along with the breakdown to the end uses (heating, cooling, fans, pumps, lights, equipment and service water heating).

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48722 Building Performance Modeling – Energy Plus

CASE 1

ENVELOPE: UDA guidelines GLAZiNG: Simple HVAC: Retail: VAV reheat Residential: Split system

CASE 2

ENVELOPE: UDA guidelines GLAZiNG: Spectral HVAC: Retail: VAV reheat Residential: Split system

CASE 3

ENVELOPE: UDA guidelines GLAZiNG: Spectral HVAC: Retail +Residential: Constant Volume DX

CASE 4

ENVELOPE: Proposed GLAZiNG: Simple HVAC: Retail: VAV reheat Residential: Split system

A

C

` B

Figure 2 – Methodology for Comparison of all Cases

Building case study description Multifamily C is a five storey building, with retail on the first floor and residential on the rest four floors. The building’s orientation is north-west with 27°tilt. The total building area is 5430 sqft and the conditioned area is 3773 sqft. The first floor is smaller in area from the rest of the floors due to the inclination of the terrain.

In the residential floors there are 9 almost equally divided apartments that lay on the east and west side. In between them there is a corridor for horizontal movement and two staircases for vertical access. The building has an unconditioned pitched roof.

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48722 Building Performance Modeling – Energy Plus

[2] Design Builder Modeling Location and Weather Data Pittsburgh with latitude N 40° 20’ and longitude W 79° 55’, falls under climate zone 5A as per IECC 2012 and has 5986 Heating Degree Days and 654 Cooling Degree Days. This makes Pittsburgh a Heating Dominant region.

CLiMATE DATA Climate Zone

5A

Latitude

N 40° 20’

Longtitude

W 79° 55’

Elevation above sea level

380 meters

Heating Degree Days

5986

Cooling Degree Days

654

Heating Dominant Climate Figure 3 : USA map showing Climate zones

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48722 Building Performance Modeling – Energy Plus The climate consultant graph above shows that only few days during summer does the temperature go above the comfort zone whereas, most of the days are rather way below the comfort zone.

Thermal Zones The building comprising of retail space on the first floor and residential units on all the four floor above was modeled in design builder. The building was divided into different thermal zones depending on the function, occupancy as well as the orientation. The retail area was sub divided into 9 zones; four corner zones and two zones on the perimeter of the long façade. An internal core zones was also specified. A depth of 5m was considered for sizing the perimeter zones along the long façade.

Each apartment units on the residential floors was divided into two zones: Bedroom (Living +Bedroom) and Kitchen (Kitchen +Bathroom). This segregation was primarily done because of the latent heat that the service area gains unlike the living or bedroom areas.

The staircase and the internal corridors were combined to create a common zone. Two such zones were created for both ends of the building. The service cores were also considered as separate zones.

The service core and the staircase zones were unconditioned. All other zones in the building are unconditioned. The thermal boundary was set at the attic of the building. Hence, the attic of the building is unconditioned.

Figure 4: Floor plans showing thermal zones

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48722 Building Performance Modeling – Energy Plus The first floor was modeled as a building component block. Part of the second floor is adjacent to grade due to the sloping landscape of the site. This part has been modeled as a building component block. The third floor and the top floor have been modeled as building component blocks too. The fourth floor and part of the second floor were modeled as the “adiabatic” blocks as they had thermal conditions identical to those modeled in the building component blocks.

Operating Schedules Four types of schedules were developed : Occupancy, HVAC (Heating & Cooling), Lighting and Equipment.

These schedules were interdependent and were made primarily based on the function of the space.

Seperate schedules were made for retail spaces and residential units. Design Builder default schedules were used for common circulation spaces and service core. Further, different schedules were made for weekdays and weekends since the occupancy differs.

1 0.9 0.8

0.7 0.6 0.5

Occupancy

0.4

Lighting

0.3

Equipment

0.2 0.1 0

Figure 5 : Retail Weekday

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48722 Building Performance Modeling – Energy Plus

1 0.9 0.8

0.7 0.6 0.5

Occupancy

0.4

Lighting

0.3

Equipment

0.2 0.1 0

Figure 6 : Residential (Bedroom + Living) Weekday

The HVAC schedules (Heating & Cooling) depended on the occupancy of the space. Whenever there was any occupancy, the heating & cooling was set on ( ratio 1.00) and whenever the occupancy was zero, the heating & cooling was set to go on set back temperature (ratio 0.00).

0.7 0.6 0.5

0.4

Occupancy

0.3

Lighting

0.2

Equipment

0.1 0

Figure 7 : Residential (Living+Kitchen) Weekday

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48722 Building Performance Modeling – Energy Plus

1 0.9 0.8 0.7 0.6 0.5

Occupancy

0.4

Lighting

0.3

Equipment

0.2 0.1 0

Figure 8 : Retail Weekend

Similar graphs were made for the weekend schedules for both retail and residential.

Assumptions Along with schedules, the occupancy , lighting and equipment densities had to be specified in Design Builder. For the residential occupancy, 3 occupants were assumed for the 2 bedroom apartments and hence the density of 0.0034 ppl/ft² (0.0375 ppl/m²) was applied. As for the retail spaces, the occupancy density was referred from CBEC standards, 0.0302 ppl/ft². As for the light power density, DOE standard was referred and for retail spaces 1.4 W/ft2 was used while residential spaces assumed 0.060 W/ft². Similarly for equipments, DOE standard was referred. The tables below show the assumptions and standards referred.

Occupancy Densities Retail

Occupancy

Residential

Standard

people/m²

People/ft²

People/m² People/ft²

Retail-ASHRAE 62.1.2004

0.326

0.0326

0.0375

Residential-Derived

0.00375

Lighting and Equipment Densities Retail W/m²

Residential W/ft²

W/m²

Standard W/ft²

DOE

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48722 Building Performance Modeling – Energy Plus Lighting and Equipment Densities

15.05

1.4

6.45

0.60

Stand Alone Retail, New Construction 2004, Version 5, Space Considered: Core Retail Front

3.23

0.30

5.335

0.50

Mid Rise Apt, New Construction, 2004

Lighting Equipment

Building Envelope Attributes (Base case) The base case assemblies were developed based on the type of construction as per UDA guidelines. These assemblies were compared to ASHRAE 90.1.10 (btu/hr ft² f). The default 30% glazing was maintained during modeling and simulation.

External Walls (Retail) Layers Thickness (in) Brickwork, Outer leaf 3.937 Air Gap 0.197 Polyethlene, Polythene 0.004 EPS Expanded Polystrene 2.362 Concrete Block (Heavyweight) 5.906 Gypsum Board 0.512 U value ( W/m²K) 0.44 U value (btu/hr ft² F) 0.078

Thickness (mm) 99.9998 5.0038 0.1016 59.9948 150.0124 13.0048 ASHRAE : 0.09

External Walls (Residential) Layers Thickness (in) Brickwork, outer leaf 3.937 Air gap 0.197 Polyethylene, Polythene 0.004 EPS expanded polystrene 0.984 Mineral fibre / wool 5.906 Woods softwood (25% bridging) Gypsum Plaster 0.512 U value ( W/m²K) 0.289 U value (btu/hr ft² F) 0.051

Thickness (mm) 99.9998 5.0038 0.1016 24.9936 150.0124 0 13.0048 ASHRAE : 0.064

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48722 Building Performance Modeling – Energy Plus Roof - Semi Exposed Ceiling

Layers

Thickness (in) 0.039 7.283 3

Roofing Felt Loose fill / powders celluloise Mineral fibre / wool Woods Softwood (15% bridging) Airgap (25 mm) 0.984 Gypsum Plasterboard 0.512 U value ( W/m²K) 0.153 U value (btu/hr ft² F) 0.027

Thickness (mm) 0.9906 184.9882 76.2 0 24.9936 13.0048 ASHRAE : 0.027

Ground Slab Layers Thickness (in) Sand & gravel 3.937 EPS Expanded Polystrene 1.181 Concrete cast - heavyweight 5.906 Rubber tiles 0.276 U value ( W/m²K) 0.902 U value (btu/hr ft² F) 0.159

Thickness (mm) 99.9998 29.9974 150.0124 7.0104 R4 as per DOE energy standards

Glazing Window Type SHGC Light Transmission Total U value

Double Low E Tint 6mm/13mm Air 0.38 0.444 0.31

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48722 Building Performance Modeling – Energy Plus

Building Envelope Attributes (Proposed case) The proposed case followed the same construction strategy as suggested by UDA for the basecase , but the type of insulation and/or thickness was changed to achieve a better U value following the Energy Saver standards from Department of Energy Exterior walls (Retail) Thickness Layers (in) Brickwork, Outer leaf 3.937 Air Gap 0.197 Polyethlene, Polythene 1.5 EPS Expanded Polystrene 3.937 Concrete Block (Heavyweight) 5.906 Gypsum Board 0.512 U value (W/m² K) 0.289 U value (btu/hr ft² F) 0.051

Thickness (mm) 99.9998 5.0038 38.1 99.9998 150.0124 13.0048

Exterior Walls (Residential) Thickness (in) 3.937 0.197 0.004 3.937 5.906

Thickness (mm) 99.9998 5.0038 0.1016 99.9998 150.0124 0 13.0048

Thickness (in) 0.039 7.283 3.937

Thickness (mm) 0.9906 184.9882 99.9998 0 24.9936 13.0048

Layers Brickwork, outer leaf Air gap Polyethylene, Polythene EPS expanded polystrene Mineral fibre / wool Woods softwood (25% bridging) Gypsum Plaster 0.512 U value (W/m² K) 0.176 U value (btu/hr ft² F) 0.031 Roof – Semi Exposed Ceiling Layers

Roofing Felt Loose fill / powders celluloise Mineral fibre / wool Woods Softwood (15% bridging) Airgap (25 mm) 0.984 Gypsum Plasterboard 0.512 U value (W/m² K) 0.136 U value (btu/hr ft² F) 0.024

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48722 Building Performance Modeling – Energy Plus Ground Slab Thickness Layers (in) Sand & gravel 3.937 Foam 3.937 Concrete cast - heavyweight 5.906 Rubber tiles 0.276 U value (W/m² K) 0.249 U value (btu/hr ft² F) 0.044 Glazing Window Type SHGC Light Transmission Total U value (btu/hr ft2 F)

Thickness (mm) 99.9998 99.9998 150.0124 7.0104

Triple Low E Tint 3mm/13mm Air 0.303 0.455 0.213

One more assumption was made during modeling and simulation that since the bedroom & living room were seperated from the kitchen and bathroom zones, Domestic Hot Water was switched off in all the bedroom zones to reduce the energy consumption.

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48722 Building Performance Modeling – Energy Plus

HVAC Systems HVAC Systems: Three different HVAC systems have been studied in the project. This includes –   

Split System No Fresh Air Single Duct VAV with Reheat Constant Volume DX

Case: The HVAC have been applied to the models in the following combinationCase 1, Case2, Case 4 –  

Split System No Fresh Air for Residential Single Duct VAV with Reheat for Retail

Case 3 – 

Constant Volume DX for Residential and Retail

Process: Case 1, Case 2, Case 4   

   

Case 1 was modeled first.

The HVAC systems were assigned to the buildings in Designbuilder itself.

The first step was to assign the appropriate HVAC system to the appropriate zone. Split System No Fresh Air needed to be assigned to each individual residential block in the model. Single Duct VAV with Reheat needed to be assigned to the retail block.

VAV Reheat was first assigned at the building level. Split systems were then individually assigned at a block level.

The HVAC modeling complexity was changed from simple to compact. The HVAC systems were also auto-sized.

The design builder default set-point and set-back temperatures were used.

The default set-point temperatures are-

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48722 Building Performance Modeling – Energy Plus 

The same procedure was applied to case 2 and case 4.

Case 3:  



 

The HVAC system was assigned to the building in Designbuilder itself.

The first step was to assign the appropriate HVAC system to the appropriate zone. Constant Volume DX was assigned to the model at the building level. The same unit was applied for the retail and the residential zone. It was applied using the Unitary Multizone option (only one unit can be applied for the whole building when using this option).

Thermostatic zone was set for the building. The zone was set to be in the residential area of the building as majority of the building has residential use. The zone was set on a typical block – Residential Floor 3 (Block 4) in the Bedroom Zone (North-East Corner). The thermostatic zone was set on a typical floor in a typical zone with representative temperature for the whole building to prevent over-heating or over-cooling in the other zones in the building.

The HVAC modeling complexity was changed from simple to compact. The HVAC systems were also autosized.

The design builder default set-point and set-back temperatures were used. These are the same as those specified in Case 1.

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48722 Building Performance Modeling – Energy Plus Understanding the Systems: The .svg diagrams created by Energy Plus after simulation were analysed for each case. The diagrams were viewed with the help of the program Inkscape. The different components and the sequence in which they are arranged in each system were identified.

SVG for Case 1 – VAV with Reheat for Retail + Split System No fresh Air for Residential

Figure 9 – Schematic Diagram of HVAC System in Case 1 created by Energy Plus

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48722 Building Performance Modeling – Energy Plus SVG for Case 4 – Constant Volume DX for Retail and Residential

Figure 10 – Schematic HVAC diagram created for Case 4 in EnergyPlus

After identifying each component and the sequence in which it is arranged, the nodes were identified in the Zone Equipment list, Air Distribution Unit, Controlled Zone Equipment Configuration etc under zone equipment section using IDFs in EnergyPlus. This information was used to prepare the nodal diagrams for the systems.

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48722 Building Performance Modeling – Energy Plus Split System with No Fresh Air ( Case 1,2 and 4 - Residential)

Figure 11- Nodal Diagram for Split System with No Fresh Air

VAV with Reheat ( Case 1,2 and 4 – Retail)

Figure 12 – Nodal Diagram for VAV with Reheat System

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48722 Building Performance Modeling – Energy Plus Constant Volume DX ( Case 4 – Retail and Residential)

Figure 13 – Nodal Diagram for Constant Volume DX

Analysis: The performance of both systems was analysed using the following metrics –    

Total Annual Energy Consumption Peak Design Loads Seasonal Energies ( Winter/Summer) Time Set-Point Not Met for Occupied Hours

Details are included in the Comparison B of Case 2 and Case 3.

Simulation parameters -

Time step for simulation was changed to 6 IDf for each model was created in Designbuilder Weather file was downloaded from Eplus website for Pittsburgh-Allehany Simulations were run for the following design days – Name of Location Day Type Maximum Dry Bulb Temperature Humidity Indicating Conditions at maximum Dry-bulb.

Day of Month Month

Pittsburgh Allegheny Summer Design Day 89F 22.5

Pittsburgh Alleghany Winter Design Day 62F -15.4

15 7

15 1

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48722 Building Performance Modeling – Energy Plus -

IDF was opened in Energy Plus Changes were made to thermostatic tolerances. Changed from 0.20 to 0.56 Inkscape was downloaded and linked to Eplus to be able to see .svg diagrams Annual and monthly simulations were run in EnergyPlus

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48722 Building Performance Modeling – Energy Plus

[3] Simulations and Results Comparison A: Case 1 v/s Case 2 These two cases have identical building envelope assemblies as per UDA guidelines and also has the same HVAC systems; that is VAV with Reheat for retail and Split System No fresh air for the residential units. The occupancy, lighting and equipment densities are identical too.

The difference between the two cases lies in the different algorithms used for specifying glazing.

First, an appropriate window was selected from the Design Builder library. Case 2 was modeled first using this window. The same window was applied for residential as well as retail. Care was taken to ensure that the window U-value and SHGC met the UDA as well as ASHRA 90.1.2010 guidelines.

For Case 1, the U-value, SHGC and Light Transmission values of the window applied in Case 2 were directly input using the Simple Method of defining the glazing assembly.

No changes were made to the time set-point temperatures, set-back temperatures, thermostatic tolerances were used for both systems. No changes were made to the summer design day and winter design day settings.

Comparison: On comparison, the following differences are seen between both cases: 

Annual Energy Consumption

The annual energy end use consumption was studied for the two cases. The graph below shows the difference between the two – CASE 2

CASE 1 Heating Cooling Lighting Equipment Fans Pumps Heat Rejection Service Water Heating TOTAL

SI [kWh] 37591.97 98806.68 315384.99 75878.89 21933.36 24075.76 1228.41 6675.11 581575.17

IP [Kbtu] 11017.12 28957.38 92430.22 22237.91 6428.03 7055.91 360.01 1956.28 170442.86

Heating Cooling Lighting Equipment Fans Pumps Heat Rejection Service Water Heating Total

SI [kWh] 36516.78 101427.16 315299.93 75878.89 21966.49 24098.53 1229.27 6675.11 583092.16

IP [Kbtu] 10702.01 29725.37 92405.29 22237.91 6437.74 7062.58 360.26 1956.28 170887.44

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48722 Building Performance Modeling – Energy Plus

Figure 14 : Annual Energy Use Comparison Figure 15 – Annual Energy End-Use Detail

Findings: It is seen that the annual energy consumption increase very slightly (0.26%) more in Case 2

as compared to Case 1.

In order to understand the end use energy distribution, the detailed break-up of energy end use consumption is studied. Energy Plus gives details for 14 categories – Heating, Cooling, Interior Lighting, Exterior Lighting, Interior Equipment, Exterior Equipment, Fans, Pumps, Heat Rejection, Humidification, Heat Recovery, Water Systems, Refrigeration and Generators. Out of these, interior lighting and exterior lighting have been combined to form one category – lighting, interior and exterior equipment have been combined to form one category – equipment. As humidification, heat recovery, refrigeration and generator values are zero for all cases (the corresponding components have not been added to the HVAC system); they have been excluded from analysis graphs.

Analysis: There was no significant difference and this can be attributed to the fact that all the

parameters were kept the same and the slight difference seen in case 2 as compared to case 1 is due to the difference in peak load calculations due to application of different calculation algorithms. 

Energy Use Intensity

The Energy Use Intensity (EUI) were studied for the two cases. The graph below shows the difference between the two –

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48722 Building Performance Modeling – Energy Plus

65

44.00

60

42.00

55

40.00

48.85

48.97 kbtu/ft²

50 45 40

38.00 36.00 34.00

35

33.94

34.03

CASE 1

CASE 2

32.00

30 CASE 1

30.00

CASE 2

Figure 16 : Energy Use Intensity Conditioned Area Comparison

Figure 17 : Energy Use Intensity Total Area Comparison

Findings: The difference in the EUI for conditioned area as well as total area in these two cases is very marginal since all the parameters are kept same.



Peak Design Load

The user design loads (peak design loads) were studied for the two cases. The graph below shows the difference between the two-

Figure 18 : Design Loads Comparison

Findings: The peak loads are marginally different for both cases since internal and external parameters like climate, light power density, etc have not been modified. 2.9% decrease in heating load and 2.6% increase in cooling load are seen in case 2 as compared to case 1. All the other loads like lighting, equipments,

fans, pumps etc did not show any change as expected.

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48722 Building Performance Modeling – Energy Plus

Analysis: The difference in peak load calculations is due to the use of different algorithms to specify the glazing assembly. In the spectral glazing method, each material is defined layer by layer. As a result, heat loads are calculated in more detail for each layer. 

Time Set Point Not Met

The Time Set-Point Not Met during Occupied Hours were studied for the two cases. The table below shows the difference between the two –

Figure 19 : Time Set Point Met During Occupied Hours for Case 1 and Case 2

Figure 20 : Time Comfortable Based on Simple ASHRAE 55-2004

Findings: It is seen that the Time-Set Point Met during Occupied Hours for case 1 and case 2 are the same since no parameters were changed.

Comparison B: Case 2 v/s Case 3 The two cases are the same in terms of functions, thermal zones, occupancy densities, lighting power densities, equipment power densities, occupancy schedules, lighting schedules, equipment schedules, heating schedule and cooling schedules. Case 2 and Case 3 have also been assigned the same envelope properties and the same glazing algorithm for heat load calculations.

However, Case 2 and Case 3 are assigned different HVAC systems. Case 2 is assigned the Split System No Fresh Air for Residential Zones and the Single Duct VAV with Reheat for Retail Zones. Case 3 is assigned the Constant Volume DX for Retail and Residential.

Hence, it is fair to conclude that the differences in the energy consumption and loads of the building are due to the different HVAC systems.

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48722 Building Performance Modeling – Energy Plus The same process was used to assign the HVAC units for both systems. The same time set-point temperatures, set-back temperatures, thermostatic tolerances were used for both systems. No changes were made to the summer design day and winter design day settings.

Comparison: On comparison, the following differences are seen between both cases: 

Annual Energy Consumption

The annual energy end use consumption was studied for the two cases. The graph below shows the difference between the two – CASE 3

CASE 2 Heating Cooling Lighting Equipment Fans Pumps Heat Rejection Service Water Heating Total

SI [kWh] 36516.78 101427.16 315299.93 75878.89 21966.49 24098.53 1229.27 6675.11 583092.16

IP [Kbtu] 10702.01 29725.37 92405.29 22237.91 6437.74 7062.58 360.26 1956.28 170887.44

Figure 21 – Comparison of Annual Energy Consumption

Heating Cooling Lighting Equipment Fans Service Water Heating Total

SI [kWh] 29580.06 187107.72 296052.39 74483.08 140865.80

IP [Kbtu] 8669.06 54835.86 86764.39 21828.84 41283.69

10349.32 738438.37

3033.09 216414.92

Figure 22 – Comparison of Energy End Use Consumption - Detail

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48722 Building Performance Modeling – Energy Plus Findings: It is seen that the annual energy end use consumption increase in the Constant Volume DX. Case 3 energy consumption increases substantially by 20.8% as compared to Case 2.

In order to understand the end use energy distribution, the detailed break-up of energy end use consumption is studied. Energy Plus gives details for 14 categories – Heating, Cooling, Interior Lighting, Exterior Lighting, Interior Equipment, Exterior Equipment, Fans, Pumps, Heat Rejection, Humidification, Heat Recovery, Water Systems, Refrigeration and Generators. Out of these, interior lighting and exterior lighting have been combined to form one category – lighting, interior and exterior equipment have been combined to form one category – equipment. As humidification, heat recovery, refrigeration and generator values are zero for all cases; they have been excluded from analysis graphs.

It is seen that maximum difference in the consumption is in the cooling and fan consumption. The cooling consumption increases by 85% in case 3 as compared to case 2. The fan usage increases by 545% in case 3 as compared to case 2.The heating consumption is higher in case 2 as compared to case 3.

The service water heating requirements are higher in case 3 as compared to case 2 also.

Analysis: In the Constant Volume DX, the volume of air being conditioned is constant. The same volume of air is conditioned irrespective of the needs of the individual zone. In this system, often more air than that which is required will get conditioned. The energy consumed by the fans increases as larger volume of air is being conditioned.

In case of the VAV with Reheat System, the dry bulb temperature inside a zone is controlled by varying the supply of air volume in the space as compared to the air temperature. At full cooling, the dampers that are in the VAV Reheat box provided in each individual zone are fully open and in case of full heating, the dampers are almost closed. Hence, the volume of air being conditioned reduces. Hence, the fans run for a shorter time and correspondingly the energy consumed by the fans decreases. In the residential zones, as each zone is assigned a separate unit, only the volume of air required by that zone is conditioned. The Constant Volume DX uses a single-speed fan where as the VAV uses a multiple-speed fan.

In the VAV system, the air supplied to the zone is heated as per the temperature required by that zone. This is done by the reheat coil in that zone. Similarly, in the split systems applied to individual zones in the residential floors, the air is heated and cooled only as per the requirements of that zone.

Hence, even though the air is heated at an individual zone level in case 2, as it is heated only as per the requirements of that zone, the energy consumed for heating is only marginally higher than that used in case 3. 

Energy Use Intensity

The Energy Use Intensity (EUI) were studied for the two cases. The graph below shows the difference between the two –

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48722 Building Performance Modeling – Energy Plus

Figure 23 – Energy Use Intensity (EUI) comparison between Case 2 and Case 3 – Conditioned Area

Figure 24 – Energy Use Intensity (EUI) comparison between Case 2 and Case 3 – Total Area

Findings: As expected, the EUI for Case 3 is higher than that of Case 2 when considering conditioned as well as unconditioned area. The EUI is 27% higher in Case 3 as compared to Case 2 in both scenarios as the ratio of conditioned area to total area is the same in Case 2 and Case 3.

Analysis: As the area of the building in Case 2 and Case 3 remains the same, increase in EUI indicates the increase in energy consumption of the building due to the application of a different HVAC system. 

Peak Design Loads

The user design loads (peak design loads) were studied for the two cases. The graph below shows the difference between the two –

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48722 Building Performance Modeling – Energy Plus

Figure 25 - Comparison of User Design Loads for Case 2 and Case 3

Findings: The peak loads, i.e., the user design loads are almost the same for both cases. This is because the different internal and external parameters (climate, envelope, lighting power densities, schedules etc) that affect the heating and cooling loads of a building have not been modified.

Analysis: As none of the parameters that affect the heat loads on the building (internal and external) were modified, it is expected that the peak loads, i.e, the user design loads which are used for sizing the HVAC system change only marginally to accommodate for the different equipment/components of both systems.

The user design loads will also be slightly different as in case 2 it is individually determined for each zone whereas in case 3 it is determined by the thermostatic zone. 

Seasonal Energy

The seasonal was studied for the two cases. The graph below shows the difference between the two –

Figure 26 – Seasonal Energy Comparison for Case 2 and Case 3

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48722 Building Performance Modeling – Energy Plus

Findings: The summer and winter energy consumption is higher for Case 2 and Case 3. The summer consumption is 42% higher in case 3 as compared to case 2. The winter energy consumption is 9.55% higher in case 3 as compared to case 2. 

Time Set-Point Not Met

The Time Set-Point Not Met during Occupied Hours were studied for the two cases. The table below shows the difference between the two –

Figure 27 – Time Set Point Met During Occupied Hours for Case 2 and Case 3

Figure 28 – Time Comfortable Based on Simple ASHRAE 55-2004

Findings: It is seen that the Time-Set Point Met during Occupied Hours is only 19% in Case 3 as compared to 99% in Case 2. Time not Comfortable based on Simple ASHRAE 55-2004 was also studied. It is seen that the time comfortable based on that is only 33% for Case 2 and 37% for Case 3. This is because changes were not made to the HVAC and Zone environmental settings to comply with ASHRAE 55-2004 standards. Hence, this value is not used for analysis.

Analysis: When assigning the Constant Volume DX System, one system is assigned to the whole building, i.e. the same HVAC system is assigned for all zones in the retail as well as the residential floors. This is applied using the Unitary Multizone option. The thermostatic zone was placed a typical residential floor in a corner unit. These cooling and heating needs for all the zones in the building are controlled by this one zone.

Hence, all zones in the building are treated as the same irrespective of their function (retail-residential living-residential service). The different internal loads (occupancy, equipment, and lighting) and corresponding schedules are not taken into consideration. Under these circumstances, it is difficult to satisfy the heating or cooling needs of all the zones.

In Case 2, each residential zone (residential living – residential kitchen) is provided with a separate Split System with No Fresh Air. Hence, the zone is heated or cooled as per its individual requirements. Even in the VAV with Reheat System which is assigned to the retail area, the conditioned air from the heating and

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48722 Building Performance Modeling – Energy Plus cooling coils is divided by the Zone Splitter and sent to the different zones in the building as per the requirements of the zone. Each zone is equipped with a damper and a thermostat in the Reheat VAV box.

The damper helps control the amount of air allowed into the zone (damper almost closed when heating required in the zone and opened when cooling required in the zone). The thermostat signals the need for heating the air. In this case, heating is provided by the reheat coil which is part of the VAV reheat system. A separate reheat coil is present in each zone to which the system is applied. This zonal control helps provide comfortable thermal conditions in the zone.

Hence, it is not advisable to use the Constant Volume DX in a mixed-use building such as this one. It may be advisable to use the Constant Volume DX for commercial applications such as office buildings which have similar loads and requirements for most zones in the building.

Comparison C: Case 1 v/s Case 4 The two cases are identical in terms of functions, thermal zones, occupancy, lighting and equipment load density, as well as in terms of schedules in occupancy, lighting, equipment, heating and cooling. Moreover, they have the same HVAC system [VAV with reheat in retail and split system no fresh air in residential] and the same algorithm in glazing.

The change between the two cases lies in the materials used. In order to achieve an improved building envelope, new assemblies were proposed. The difference between the assemblies of Case 4 compared to the ones of Case 1 is the increase of the thickness of the insulation layer, which is translated in decrease of the U-Value.

As only the insulation thickness was changed throughout the whole building envelope between cases 1 and 4 it is logical to assume that the differences in energy consumption and loads of the building are due to the increase of thermal resistance and tightness.

Comparison: On comparison, the following differences are seen between both cases: 

Annual Energy Consumption

The annual energy end use consumption was studied for the two cases. The graph below shows the difference between the two – CASE 1 Heating Cooling Lighting Equipment Fans Pumps

CASE 4 SI [kWh] 37591.97 98806.68 315384.99 75878.89 21933.36 24075.76

IP [Kbtu] 11017.12 28957.38 92430.22 22237.91 6428.03 7055.91

Heating Cooling Lighting Equipment Fans Pumps

SI [kWh] 4127.66 96945.6 313445.03 75878.81 24988.69 24070.35

IP [Kbtu] 1209.70 28411.95 91861.67 22237.88 7323.46 7054.32

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48722 Building Performance Modeling – Energy Plus Heat Rejection Service Water Heating TOTAL

1228.41

360.01

6675.11 581575.17

1956.28 170442.86

Figure 29 – Comparison of Annual Energy Consumption

Heat Rejection Service Water Heating Total

914.69

268.07

6675.11 547045.94

1956.28 160323.34

Figure 30 – Comparison of Energy End Use Consumption - Detail

Findings: As it was expected, it is seen that the annual energy consumption decreases in case 4, where the building envelope is more insulated. Case 4 energy consumption decreases substantially by 6% as compared to Case 1.

It is seen that maximum difference in the consumption is in the heating consumption. The heating consumption decreases by 89% in case 4 as compared to case 1. Cooling consumption decreases marginally.

Analysis: In Case 4, the proposed assemblies have significantly lower U-values, hence the decrease in heating consumption is well explained. However, the cooling consumption is not affected that drastically as the SHGCof the proposed glazing assembly is only marginally lower than that used in the base model. 

Energy Use Intensity

The Energy Use Intensity (EUI) were studied for the two cases. The graph below shows the difference between the two –

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48722 Building Performance Modeling – Energy Plus

Figure 31 – Energy Use Intensity (EUI) comparison between Case 1 and Case 4 – Conditioned Area

Figure 32 – Energy Use Intensity (EUI) comparison between Case 1 and Case 4 – Total Area

Findings: As expected, the EUI for Case 4 is lower than that of Case 1 when considering conditioned as well as unconditioned area. The EUI is 6% lower in Case 4 as compared to Case 1 in both scenarios as the ratio of conditioned area to total area is the same in Case 4 and Case 1.

Analysis: As the area of the building in Case 4 and Case 1 remains the same, decrease in EUI indicates the decrease in energy consumption of the building due to the increase of the insulation thickness in the roof, wall and slab assemblies as well as the decrease of the U Value of the glazing.

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48722 Building Performance Modeling – Energy Plus

[4] Conclusions The aim of this assignment was to analyze and compare different HVAC systems and two different glazing algorithms (simple and spectral) in a base case and proposed case. The models were designed in Design Builder using UDA guidelines for envelope assemblies, proposed assemblies, operating schedules developed and the different HVAC systems option (VAV reheat for retail, Split with No Fresh Air for residential, Constant Volume DX for the entire building).

Four building cases were modeled using Design Builder: Case 1 – Base case (UDA guidelines envelope) + simple glazing + base HVAC (VAV for retail + Split for residential), Case 2 – Base case + spectral glazing + base HVAC, Case 3 – Base case + spectral glazing (layer by layer) + alternate HVAC ( Constant Volume DX for entire building) , Case 4 – Proposed case (envelope assemblies) + simple glazing + base HVAC. These models were then transferred to Energy Plus to conduct monthly, seasonal and annual energy simulations.

Comparisons were made between: Case 1 & 2, Case 2 & 3 and Case 1 & 4.

According to the simulation results, there was not much difference in Annual Enery Utility Intensity between case 1 and 2 since no parameters were changed other than the glazing algorithm. The EUI in case 3 was more than case 2 due to the Constant Volume DX system in case 3. EUI was considerably less in case 4 than case 1 since the envelope assemblies in case 4 were better in thermal performance.

From this study, it can be concluded that better thermal performance envelope reduce the overall energy consumption and especially the heating loads which is an important factor to be considered for Pittsburgh climate. It is also evident that Constant Volume DX system is very inefficient and more energy consuming since it depends on a single thermostatic zone whereas Split No Fresh Air with VAV Reheat was a lot more efficient. Overall, choosing efficient HVAC system reduces the energy consumption considerably. This has more effect on the energy consumption of a building as compared to increasing the thermal performance of the envelope assembly. From the modeling point of view, it has been observed that the layer by layer glazing algorithm (spectral) is a more precise method than simple glazing algorithm. Generally speaking, it is important to use the same algorithm for different models while comparing the cases, since different algorithms give slightly different results.

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[5] References ASHRAE (2010). ASHRAE STANDARD 90.1 -2010 - Energy Standard for High-Rise Buildings DOE Reference Building Models for New Construction Mid-Rise Apartments 2004 Design Builder program website: http://www.designbuildersoftware.com (Last Accessed: December 09,2011)

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