Heat pump water heaters

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Natural Resources Canada tested heat pump water heaters in its side-by-side test homes in Ottawa.

By Bruce Nagy

Markets are changing relatively quickly in the clean energy sector. Electricity generation from renewables is expected to grow about 46 percent globally during the next five years, and electric vehicles seem to be taking off. Buildings are becoming greener too.

In the HVAC business heat pumps are making significant inroads and, perhaps surprisingly, heat pump water heaters (HPWHs) are also starting to show some growth.

Just a few years ago General Electric (GE) introduced its Geospring heat pump water heater that went south due to lack of sales. But in 2019 it’s different. Sales are growing at more than eight percent in North America and more than 11 percent globally, according to research companies Research and Markets and Technavio, respectively. This growth rate is expected to continue for the next five years, at least.

 

This U.S. Department of Energy schematic shows the major components of a typical heat pump water heater.

Consumers slow to accept

It’s surprising because HPWHs remain expensive relative to conventional water heaters. That was the rationale GE offered when it surrendered and withdrew its Geospring product from the market in 2016. It said homeowners were not convinced of the value, despite the fact that utility savings recovered the extra cost within about three years, and there are usually cash incentives available.

One happy customer was builder Dave de Sylva of Howland Green Homes in Markham, Ontario. He installed Geospring units in the mechanical rooms of net-zero condominium buildings, locating them in close proximity to solar inverters, which emit heat. This same set-up was used by Reid’s Heritage Homes in its net-zero detached homes in Guelph, Ont., using Rheem heat pump water heaters.

Up and down market

Like other heat pump water heater manufacturers, Rheem endured the ups and (mostly) downs of the product for years and is finally benefitting from its patience, and the changing market. “There is an encouraging amount of interest,” reported Mark Muzyka, Rheem national sales manager – residential water heating. “We had the early adopters who jumped on it at the beginning, but at this point we are starting to get a stronger foothold within the mainstream market.”

The company is seeing growth in both individual purchases and block installations. Modern HPWHs have improved to the point where the Rheem unit now has an efficiency factor of 3.50, Wi-Fi capability, and leak detection alerts. It uses R410A refrigerant.

The builder chose Rheem Prestige Series heat pump water heaters for a net-zero development in Guelph, Ont.

A.O. Smith and Bradford White also offer heat pump water heaters. The A.O. Smith Voltex comes in 50, 66 and 80-gallon models and offers an energy factor of 3.42. Bradford White’s Aerotherm 50 and 80-gallon models are listed at 3.39 and 3.48 respectively.

NRCan research project

A few years ago, the Canadian Centre for Housing Technology (CCHT) decided to do some testing on HPWH energy savings. CCHT is a project of the National Research Council that undertakes studies using two identical houses, which were built side by side for this purpose in Ottawa, with support from the Natural Resources Canada (NRCan) and the Canadian Mortgage & Housing Corporation (CMHC).

They meet the R2000 standard and the Net-Zero-ready standard (currently connecting solar PV). They have triple pane windows, R24 bats in the wall cavities, R10 rigid foam outside for continuous walls, and R75 in the attics, reported team leader Heather Knudsen.

NRCan research engineer Martin Thomas used the two-house test facility to compare HPWHs from General Electric and AO Smith to conventional electric water heaters. “We found that the heat pump water heaters use about one third as much energy as the older technology.”

One of his reports says: “Compared to the standard electric resistance water heater, the heat pump water heaters operated at lower power for longer cycles. Heat pump water heater A had a power draw of ~1000 W, heat pump water heater B had a power draw of ~500 W, whereas the electric resistance water heater had a power draw of ~4000 W.

In winter, the heat pump water heaters consumed, on average, 5.0 kWh/day, a 61 percent energy savings compared to the conventional electric water heater.

In summer, the heat pump water heaters consumed on average 4.3 kWh/day, a 60 percent energy savings compared to the conventional electric water heater.” This finding more or less verifies the three-year payback in Geospring’s old ads. Rheem’s current HPWH marketing promises savings for homeowners of $4000 over the life of the product.

It is important to note that heat pump water heaters don’t directly generate heat. They work like a refrigerator in reverse, taking heat from the surrounding air and dumping it at higher temperature into the tank, thus heating the water. They use electricity to move heat from the indoor space into the tank. So, while the efficiency numbers are substantially better than a conventional electric water heater, that is offset somewhat by the reality that this “scrounged” heat is putting an extra load on the furnace or boiler.

The designer chose a Midea heat pump DHW heater for an Owen Sound, Ont. passive house.

Thomas writes: “As expected, the savings in energy use for water heating was offset by an increase in furnace energy consumption for heating…(and) the impact of the heat pump water heater on whole-house energy balance is considered insignificant…In summer, a small secondary impact on energy for operating the air conditioning system was seen.”

Some critics have questioned whether a water heater scrounging for indoor heat in the winter makes sense, insofar as the absorbed heat energy might simply need to be replaced by the space heating system, eliminating energy savings. On the other hand, in the summer everyone we talked with seems to agree that the HPWH saves about 20 percent on cooling energy.

Space requirements

At a time when residential mechanical rooms are becoming smaller or non-existent, a heat pump water heater needs space to be able to absorb heat from the air. “You have to be careful not to enclose your (heat pump) unit in a closet,” said Muzyka. To be effective they need 100 square feet around them (and, as mentioned, perhaps some heat-emitting solar inverters nearby).

In a passive house built this year near Owen Sound, Ont., designer Rob Blakeney did put a Midea heat pump water heater in a closet. However, he created long louvers so that it could draw heat from the adjacent living room and then the cool outgoing flow was ducted into a bedroom.

There was another option, he added. “This “parasitic” aspect is avoided by the Sanden CO2 Heat Pump, which has an outdoor evaporator unit, and extracts heat from outside air…in addition to producing hot water, it can be used for some supplementary heating (approx. 10-14,000 BTU/h) via a hydronic coil.”

He is considering the Sanden unit for a project in Guelph, Ont. “It’s a whole different level of appliance, with its added space heating capability (and high price) and it is a good option for the right kind of super-insulated project with a smaller overall energy load.” He’s also planning to import an even more capable European combo unit for an upcoming Toronto passive house.

With HPWHs and heat pumps breaking sales records, smaller, tighter, more electrified homes, increasing performance co-efficiencies, decreasing energy loads, and new approaches for meeting them, it might be time for a tag line like: “Go green in 2019.”

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