Air to Water Heat Pumps

Benefits

Reduced Energy Consumption

  • Extracts more units of energy from the air (in the form of heat) than it consumes (in the form of electricity).
  • Supplies both space heating and space cooling as well as water heating.

Reduced Energy Costs

  • Reduces utility bills by producing 2 to 5 kilowatts of heat energy for each kilowatt it consumes.
  • Replaces or augments existing space heating and cooling systems.

Reduced Environmental Impact

  • Lowers emissions.
  • Reduces consumption of non-renewable fuel resources.

Reduced Installation Requirements

  • Works with existing furnace ductwork, radiators, baseboard convectors or in-floor hydronics.

Description

  • An air-to-water heat pump extracts heat energy from the outside air. An outdoor heat exchanger coil extracts the heat energy and an indoor heat exchanger coil transfers the heat to the end use. Sensors and controls allow the heat pump to supply year-round domestic hot water as well as seasonal space heating and cooling. Some systems can also provide dehumidification.
  • Space heating can be delivered by forced air (fan coil) or by hydronics (baseboards or in-floor).
  • While new in Canada, air-to-water heat pumps are popular in Europe and Japan.
  • The efficiency of a heat pump is measured by the coefficient of performance (COP). The COP is the energy output of the heat pump divided by the amount of electricity needed to run the unit. Another measure of efficiency is the heating seasonal performance factor (HSPF). The HSPF is the total heat output during the heating season divided by the total energy used during that time. This number is similar to the seasonal efficiency of a fuel-fired heating system. For cooling, the measure of efficiency is the Seasonal Energy Efficiency Ratio (SEER). The higher the COP, the HSPF or the SEER, the more efficient the unit.
  • A new generation of heat pumps have been designed specifically for cold climates. Heat pumps lose efficiency when outdoor temperatures drop. Most heat pumps installed before 2010 required a backup heating source or had to be over-sized to provide 100% of the space heating needs. Performance has been improved by using variable capacity compressors with ‘inverter’ technology. As temperatures drop and the first stage or low speed cannot meet the required comfort level, the second stage or high speed activates. Other improvements include more efficient blowers and motors; larger coil surface areas; time delays on controls; and expansion valves to control the flow of the refrigerant more efficiently. These new ‘Cold Climate’ heat pump systems can supply most or all of a home's heating needs without back-up for weather conditions as cold as -20°C.

Figure 2 — Outdoor Air Source Heat Pumps Condenser Units — Harmony House  EQuilibrium™ home

Two air source heat pumps are located beside the exterior side wall of a house.

Two air source heat pumps are located beside the exterior side wall of the Harmony House EQuilibrium™ home.

Design/Installation/Operation/Maintenance Considerations

  • Professional installation is required.
  • These units are new to the market and do not have an ENERGY STAR category. Look for a HSPF above 9 or a COP above 3.
  • Outside unit should be located away from prevailing winds, but in a clear area so there is free air flow around the whole unit and it can be easily serviced. Avoid placement under roof drip lines or where the unit may be blocked by snow drifts.
  • The outside unit must be installed on a stand so that it is above expected snow depths.
  • If the outside unit is to be installed in the side yard between two houses, consider the quietest-running units in your purchase decision, as the space enclosed by the adjoining walls can amplify the sound of the equipment in operation. Sound-deadening baffles are also available to reduce the noise level.
  • The unit must be sized properly based on actual heat loss, heat gains and projected demand for domestic hot water to take full advantage of the energy savings. Best practice is to have a room-by-room heat loss/heat gain calculation done.
  • Ensure the installation package includes a condensate drain for the indoor coil that complies with manufacturer specifications and local codes, an air filter package, and that all exposed ducts and plenums are to be taped or sealed to minimize air leakage.
  • In colder temperatures, the efficiency of a heat pump goes down. New ‘cold climate’ heat pumps promise much better performance at temperatures below -25°C. An air-to-water heat pump feeding a low-temperature hydronic system may be more appropriate in colder climates, as the amount of low-level heat that can be supplied is a close match to the demand temperature of the delivery system.
  • Look for units with variable capacity compressors, or dual compressors for highest operational efficiency.
  • Ozone-friendly R410A refrigerant is used in most current models.
  • Ask your installer for all documentation and instruction on how to operate thermostats and any other controls, and what the proper service and maintenance schedule should be.

What Does it Save?

The cost savings associated with the replacement of a conventional furnace or boiler and hot water tank with air-to-water heat pump is dependent upon a number of factors including the efficiency, condition and location of the original equipment, existing energy type and cost, and the climatic region.

Here is an example of the possible savings for space and water heating that a family of four could see with an air-to-water heat pump. The example family lives in a 2-storey house built in 1973. The air-to-water heat pump in this example is a 13 kW all-electric unit with a HSPF of 10, and ties into the existing ductwork for a forced-air system. It replaces a mid-efficiency gas or oil furnace, or electric baseboard heat. The charts shows the estimated savings associated with space and water heating only. Notice that there are deep energy reductions to be had in all parts of Canada, but the annual energy cost savings vary widely. Where the current cost of gas is low and electricity is high, as in Calgary or Toronto (2012 costs), changing out a natural gas furnace and gas hot water tank will result in a net increase in annual space and water heating energy costs. However, where both gas or oil and electricity are higher priced (as in Vancouver, Montreal and Halifax), changing out a furnace results in a significant reduction in annual costs associated with space and water heating. None of the charts include air conditioning energy use or costs. In areas with high air conditioning needs, energy and cost savings will be different.

Replacing Oil Furnace (83% eff.) + Electric Water Heater with Air-to-Water Heat Pump

Replacing Oil Furnace + Electric Water Heater with Air-to-Water Heat Pump
  Toronto Halifax
Existing Megajoules/year 36,814 48,129
A2W Megajoules/year 14,291 16,424
$ Annual Savings 2,596 3,203

Replacing Electric Baseboard + Electric Hot Water with Air-to-Water Heat Pump

Replacing Electric Baseboard + Electric Hot Water with Air-to-Water Heat Pump
  Vancouver Calgary Toronto Montreal Halifax
Existing Megajoules/year 31,732 35,490 31,926 34,753 40,008
A2W Megajoules/year 10,080 17,802 14,291 19,844 16,424
% Reduction in Energy use 68 50 55 43 59
$ Annual Savings 559 555 681 286 963

Replacing Gas Furnace (78% eff.) + Gas Hot Water (58% eff.) with Air-to-Water Heat Pump

Replacing Gas Furnace + Hot Water with Air-to-Water Heat Pump
  Vancouver Calgary Toronto Montreal
Existing Megajoules/year 44,310 50,442 44,797 44,325
A2W Megajoules/year 10,080 17,802 14,291 19,844
% Reduction in Energy use 77 65 68 55
$ Annual Savings 1,128 -623 -213 1,058

The information contained in this publication represents current research results available to CMHC. Readers are advised to evaluate the information, materials and techniques cautiously for themselves and to consult appropriate professional resources to determine whether information, materials and techniques are suitable in their case. The text is intended as general information only and project and site-specific factors of climate, cost, aesthetics, practicality, utility and compliance with applicable building codes and standards must be taken into consideration. A number of assumptions were applied with respect to fuel prices, water rates, costs of materials, equipment and labour, planning horizons, etc. Actual reductions in energy consumption and fuel savings will vary. Any reliance or action taken based on the information, materials and techniques described are the responsibility of the user. CMHC accepts no responsibility for consequences arising from the reader’s use of the information, materials and techniques herein.

Last revised: 2013

Canada

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