Harnessing nature

Hydronic heating and cooling technologies use earth and air as energy sources, as these two Stiebel Eltron case studies demonstrate.

Reducing the energy demand of residential buildings has become a key focus area of the ongoing effort to shift towards a more energy-efficient future. Heat pump technology is evolving rapidly, causing builders to take notice as the technology improves and becomes more affordable—particularly when you consider that nearly 80% of the energy consumed in the home is used for heating and hot water. The following case studies look at two increasingly popular and efficient hydronic heating technologies used in New Zealand homes.

Geothermal heat pumps

Geothermal heat pumps, also known as ground-source heat pumps, utilise energy harvested from the ground to provide hydronic heating, cooling and hot water efficiently. These heat pumps achieve a high coefficient of performance due to the stable temperature of the Earth’s surface.

According to Marti Smith, director at Heated in Arrowtown, consumer awareness and uptake levels of geothermal heat pump technology varies.

“While there’s quite good consumer awareness of the technology, there’s also a resistance to commit as most Kiwis are building for profit. However, most of my clients are building dream or retirement homes and are happy to spend to save.”

Typically, the capital cost on geothermal heat pumps is higher, but so are the savings—and they’re instant. According to Heated client Jeff Desbecker, who installed geothermal heating in his approximately 450m2 new build in Lake Hayes, he was able to enjoy lower energy AUTHOR: CLARISSA VAN EMMENES

Three 80m deep boreholes were needed for this geothermal hydronic heat pump installation for underfloor and radiator heating.

on the location, installation may require resource consent as drilling is involved.

“Most of our clients install the systems on rural properties with a bigger land area and are typically building bigger, long-term homes,” says Marti.

The local climate will give you an indication of the average incoming water temperature to the heat pump over the year, which helps with planning the size of the captor loops or borehole depth. Climate typically doesn’t affect pump performance.

GEOTHERMAL HEAT PUMP QUICK FACTS

Low-temperature fluctuations throughout the year in the ground Heating output throughout the year virtually constant Performance efficiency constant irrespective of outside temperature No defrosting of evaporator required.

One of the smaller geothermal heat pumps installed at Jeff Desbecker’s Lake Hayes project.

bills almost immediately and just in time for winter in 2020.

“The property is built on an approximately 1.5 acre site, with two residential flats and a 3-bedroom main house. So we have three different building platforms with three separate demand units and varying demands on the system.

“Marti helped us set up controls in every room, and they were able to design a system that would work for our soil. We enjoyed going through last winter with plenty of hot water and heat in a large house with high ceilings.”

Installation

The heat pump unit is located in a plant room, usually inside the building. According to Marti, this typically requires negotiation with home owners and architects at the beginning of the project to allow space in the floor plan.

Integrating ground source heat pumps into a new build property is straightforward when the ground works are underway, while system optimisation ensures the heat pump will always perform at maximum efficiency to minimise energy consumption.

The challenge when installing a geothermal heating system on a tight residential site is that it uses boreholes, which can add some expense to the project.

“If the site has a lot of land, horizontal captor loops can be used to a depth of 1.2 to 1.5m—usually between two to three times the area of the house is required,” says Marti.

The Lake Hayes property didn’t have the option to drill, so the team had to lay 1000m of pipe in the ground.

Location, location, location Why go geothermal?

A geothermal heat pump is one of the most sustainable and cost-efficient heating/cooling systems currently on the market. Given its capacity for providing a different range of services, such as heat generation, hot water, proper humidity levels and air cooling, it has the potential to become the heating system of choice for many future consumers.

Whilst still a bigger upfront cost, prices for ground source heat pumps are decreasing from year to year due to successive technical improvements.

Air source heat pumps

Air source heat pumps (ASHPs) absorb heat from the ambient air to heat a home and its hot water. They can extract heat from air even when air temperatures are as low as -25°C.

Like all other types of heat pumps, air source heat pumps need electricity to run the compressor. However, as they extract a large part of renewable heat from the environment, the heat output is greater than the electricity input. As a result, the heat pump achieves an excellent ratio between ‘harvested’ heating energy and consumed primary energy.

“An air source heat pump enables over four kWh of heating energy to

be generated using one kWh of electrical energy—making it over 400% more efficient than the direct electrical heating,” says Jonathan Toulsen, director at H2Flow Plumbing and Heating in Christchurch.

The inverter technology used in air source heating systems will always deliver the precise output required at any given time. This greatly adds to its energy efficiency, and also helps reduce noise emissions during seasons when the fan operates at a lower output.

Installation

Air source heat pumps are simpler to install than ground source heat pumps, which makes them more affordable when modernising an existing heating system.

“We have options to choose from to suit any demand—from small units through to apartment blocks and commercial buildings,” says Jonathan. “So it’s a really good solution whatever the situation.”

The heat pump is typically located outside the house. A circulating pump transfers the energy from the heat pump into the buffer tank, which then circulates it into underfloor pumps or radiators. Domestic hot water can also be produced via a coil and sensor in the domestic hot water cylinder.

Location, location, location

Tauranga homeowner Jamie Wentzel has found air source hydronic heating to be perfectly suited to his environment and home. Jamie’s house is older, built almost 50 years ago, and used an old, inefficient oil burner for heating during winter. The mild winters and hot summers proved well suited for an air source heat pump.

According to Jonathan Toulson, most of New Zealand is well-suited for air source heating. For old homes like Jamie’s, no

AIR SOURCE HEAT PUMP QUICK FACTS

Operates at quarter of the cost of conventional heating Can provide up to four times as much heat as an electric heater Good longevity, being able to run for over 20 years Ductless versions available for homes without ducts.

Air source heat pumps can provide the energy for underfloor and radiator hydronic central heating systems.

Owners have options for indoor or outdoor installation of air source heat pumps.

building consents are needed, which makes it an even more convenient option. “Retrofits are typically fine unless you’re installing a domestic hot water cylinder— then this will have to have a building consent,” says Jonathan.

“With new builds, the pump will need to be included in the plans and specifications being submitted for consent.”

Why go with air source heating?

Like many energy efficient technologies, the upfront cost of air source heat pumps is higher, due to the more complicated installation. However, as homeowner Jamie Wentzel notes, “The running costs are so low and we have been able to see a return on investment within four years.”

Upfront cost can be reduced depending on which heat pump customers go with. “Units with a reversible refrigerant cycle are often cheaper,” says Jonathan. “This also ensures that the house will be heated in winter and cooled in summer.

“Generally an additional split air conditioning system has to be installed for cooling, but recent installations in many parts of the country have shown that, when suitably sized hydronic heat pumps are chosen during the design phase, the house can be cooled either via underfloor or fan coils.

“Cooling with fan coils is more effective than underfloor cooling. Fan coils can be fed with much lower temperatures whereas the circulating water temperature in the underfloor pipes depends on the humidity level of the room.”

With greater awareness around reducing the heat loss from a home with wall and ceiling insulation, edge insulation and higher spec windows, homeowners are increasingly taking notice of the financial and environmental benefits of efficient heating and cooling technologies.

About Stiebel Eltron: Stiebel Eltron, which provides both geothermal and air source installations, has seen its market share grow significantly in the renewable energy sector, and is focusing on educating the market via hubs and training sessions, whilst also helping homes and businesses make the shift towards renewable energy to support the Government’s climate goals for 2030.