The promise of water-source heat pumps

About half to two-thirds of the average Western Washington home’s energy use is for space heating and cooling, and water heating. Normally, temperature management is either accomplished by burning gas or propane, or by using an electric resistance heater or air-source heat pump.

There’s another, more energy-efficient option: Water-source heat pumps. These systems operate on the same basic principles as other heat pumps. They transfer heat from one side of the system to the other. In an air-source heat pump (an air conditioner with a valve that allows it to operate in both directions instead of just one), the outside air acts as the heat source in heating mode, and as the heat sink in cooling mode.

In a WSHP, water from a natural or artificial water body is the heat source or heat sink. WSHPs can produce three to five times as much thermal energy as the electrical energy they consume, by taking advantage of the physics involved in the phase change of a working fluid which is contained within the system. The high efficiency is due to the very good thermal contact between the heat exchange fins and the water, and the relatively stable temperatures of water bodies. Heat from a WSHP can be used for space heating or for water heating.

In other words, a water-source heat pump can use as little as 20% of the energy of a conventional fuel-burning or electric resistance heating system. In locations where they can be used on a large scale, their use might be the single most effective way to reduce both total home energy use, and the amount of fuel used for home heating and cooling. The technology has been commercially proven in Europe on a large scale. WSHP district heating systems are used in Drammen, Norway (population 100,000), Stockholm and Paris.

The feasibility of WSHPs is dependent on the availability of a large water body with stable temperatures. Here in La Conner, we are adjacent to Puget Sound and the Swinomish Channel. Furthermore, we are in a climate in which we need more heating than cooling. If we used large-scale WSHPs, we would be taking more heat out of the water during heating season than we would be putting in during cooling season. The total amount of heat required for all buildings in La Conner, Shelter Bay and Swinomish Village would probably be too low to significantly affect water temperatures. However, if the effect was noticeable, it would be in the direction of removing heat from the water, which would be helpful for marine life.

The installation of WSHP systems is capital-intensive, due to the need for heat exchangers, water intake systems and infrastructure for distributing thermal energy. To make the most effective use of a WSHP system, the community would probably need to create a district heating system, by which the heat distribution system could be extended to as many buildings as possible. This might be done, for instance, by creating a district heating/cooling cooperative, which would install and manage the system, and would thus operate as a heating and cooling utility. The capital and operating costs of such a system would be paid through savings on gas, propane, electricity and maintenance of independent heating/cooling systems.