Water-Water Heat Pumps

Advantagesy

• high heat factor
• short payback period
• lower acquisition cost

Disadvantages

• lack of suitable locations
• chemical composition requirements

How does a water-water heat pump work?

The natural source of heat used for the operation of this type of system is surface, underground or subterranean water. The water which is collected from a source (in most cases a well) passes through the heat pump's exchanger (evaporator), which removes some of its heat. The chilled water is then returned back to the source through a second (suction) well. The distance between the two bore holes should be at least 10 meters with the underground current ideally flowing in the direction from the source well to the suction well.

For those who have such conditions, a water-water based system is usually the preferred heat pump choice. The creation of the water source is usually inexpensive because, in most cases, the well is already there.

The efficiency of water-water heat pumps:

This is the most efficient type of heat pump on the market. This is because underground water maintains a constant temperature of approximately 10 °C throughout the year (the temperature of the water is not affected by the temperature changes at the surface). It is therefore also the warmest available source of energy for this type of use. The heat factor usually ranges about 6, which means that a water-water heat pump can save you up to 80% in operating costs.

Capacity sizing of water-water heat pumps:

The capacity of water-water heat pump is sized in a manner similar to that used for ground-water type heat pumps – i.e. the heat output of the pump should correspond to 70% of the building's total heat loss.

Heat Source Requirements

Well Version

The heat pump will require a natural water source with a sufficient yield. For an average-size family home, the average yield is approximately 0.5 l/s.

The yield of the well has to be calculated through a hydrogeological survey using an aquifer test. During this process, water is pumped out of the well for 14 days at the required flow rate using a submersion pump. If the well is not emptied during this period and if the water level in neighboring wells also remains unaffected, the water-water based heat pump system can be installed in such a location. The permit to use the underground water is obtained based on the results of the aquifer test.

River, Lake, Etc. Version

The heat, which is removed from the water, is once again used to power the system in the case of this configuration. Unlike the well-based system however, the disadvantage of the river or lake based system is the fact that for a large part of the year, the temperature of the water source remains below the 5 °C level, which prevents the ability to directly chill the water any further. This is why the system is equipped with a heat exchanger (made of polyethylene or PE hosing), which is placed into the bed of a river or a lake and filled with an antifreeze coolant.

This type of installation must be approved by the authority managing the respective water source (usually the river management authority for the given territory, the environmental reclamation authority or the local municipality). Although the use of this particular type of system is not very common, it usually provides an excellent source of energy. A very accurate calculation of the water flow is however required in order to accurately size the capacity of the heat exchanger, which is to be placed into the water. Such a calculation has to be professionally done.