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Water Source Heat Pump Systems


Water source heat pump systems consist of multiple water source heat pump (WSHP) units, a building piping loop, cooling tower, and boiler. The WSHP units themselves are water-to-air heat pumps comprised of a compressor, water/refrigerant heat exchanger, airside coil (refrigerant/air heat exchanger), reversing valve, fan section, filters, drain pan, and cabinet. WSHP units are available in many configerations including horizontal units for above the ceiling applications, small and large vertical units, rooftop units, and console units. All the unit configurations except the console units
require a ductwork system for delivering conditioned air to the space. Console units are rarely ducted through the outside wall for ventilation air in this climate because air entering the WSHP units should be above 60° F. (15'C)

Water Source Heat Pump (WSHP) systems are one of the most efficient, environmentally friendly ways to heat and cool buildings because each unit responds only to the heating or cooling load of the individual zone it serves. These systems are ideal for office buildings, hotels, health care facilities, banks, schools, condominiums and apartments.

Water source heat pumps remain a revolutionary concept for their simplicity and outstanding energy performance.

Water source heat pump (WSHP) systems share the ability to move energy from where it is not needed to where it is needed with other sophisticated HVAC systems. The nergy is moved in water, which is very effective and requires minimal transport (pump) work.

Figure shows how WSHPs can move energy around a building. In a WSHP system, high efficiency, self-contained units can be placed in virtually any location within a building and connected via a water loop. Heat is added and rejected from the loop using a boiler and cooling tower, or by using natural sources such as the ground, a well or a pond. Each unit esponds only to the individual cooling or heating load of the individual zone they serve. This results in close control over the temperature and humidity in each building zone, which leads to excellent occupant comfort. Energy use is kept to a minimum because units will generally only operate when there is a call for heating or cooling in their specific zone. In fact, in milder ambient conditions, the units may operate for only a short period of time during occupied hours.

Building Water Loop:

Each zone or space will have one or more WSHP units which are connected to a two pipe water loop (one supply pipe and one return pipe). The heat pump units either reject heat to or extract heat from the piping loop depending on whether they are cooling or heating the space. This system will therefore recover and redistribute heat when some of the units are in the heating mode and other units are in the cooling mode. This is an advantage particularly where there is an interior building core which requires year around cooling, and a perimeter zone where heating is required in the winter. Rejected heat from daytime cooling requirements can also be used for nighttime heating requirements when thermal storage is provided.

The Advantages of Using Water

Water is the most efficient way to move thermal energy. For example, a 51 mm water pipe can carry the same amount of cooling as a 610 mm air duct, requiring up to 90% less transport energy in the process and taking up far less space. The mass of the water loop also provides thermal storage, allowing a substantial amount of heat to be carried from occupied periods into morning warm-up. There is no storage benefit in most HVAC systems.

Water-source heat pump heat exchangers are more compact and efficient than air-cooled heat exchangers because the much higher mass and thermal conductivity of water, providing closer approach temperatures and higher heat pump efficiencies. Water-source heat pumps also operate at lower condensing temperatures because they are linked to the outdoor wet bulb temperature (using a cooling tower) or the deep earth temperature (using a ground heat exchanger) instead of the higher outdoor dry bulb temperature, again leading to higher efficiencies and longer s

The piping loop is kept between 60° F(15'C) and 90° (32'C) pump operation. The piping loop therefore does not need to be insulated which is a cost savings.

 

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Water source heat pump (WSHP) systems operation modes.
 
Water source heat pump (WSHP) systems typical installations
 
Water source heat pump (WSHP) systems manufacturers
 
Advantages of WSHP Systems:

WSHP systems provide good zoning capability, each unit can provide cooling or heating irregardless of what the other units are doing, or whether the rest of the building is in occupied mode or
not. Small horizontal ceiling units can be relocated easily, or added as needed for changing building or tenant requirements. If a unit fails, the rest of the system remains operational (unless the boiler or cooling tower fails). Electrical energy use for the individual heat pump units can be metered for each tenant to recover at least a portion of heating and cooling costs (does not include the pumping, boiler and cooling tower operating costs). The installed cost of WSHP systems is lower than most competing systems, particularly two and four pipe fan coil systems because of savings in piping, pipe insulation, and control costs.

 
Disadvantages of WSHP Systems:

The primary disadvantage of WSHP systems is added maintenance. A typical system will have a large number of small heat pump units, all of which require maintenance, and repair or replacement as units fail. A WSHP unit is more complex and has more moving parts than a simple fan coil unit. In addition, the cooling tower is prone to freezing, and requires winterization. Cooling towers themselves are an added and often "strange" maintenance item.

 
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