Heat Pump (Water-To-Air) - Bard MULTI-TEC W18AAPA Service Instructions Manual

The length of the defrost cycle will vary depending upon actual outdoor temperature, humidity levels
and amount of accumulated frost. It could range from 1-2 minutes up to but not exceeding 10
minutes. When the defrost cycle terminates, the reversing valve will shift back to heating mode and
the outdoor fan will restart. There is typically a large puff of steam emitted as the fan restarts.
When the heat pump shifts from cool to heating mode, from heating to cooling mode, and especially
during defrost cycles, there will be a pressure transfer sound heard as the reversing valve redirects
the flow of refrigerant. This is commonly described as a hissing noise and is a normal sound for this
type equipment.
For air source heat pumps, it is important to keep heavy snow from accumulating around the
machine to the point of blocking the inlet and outlet openings to the outdoor coil section. For wall
mounted or other equipment that is elevated, this should not be a factor; but for equipment installed
on or near the ground, this can be an issue in areas prone to heavy and/or blowing snow. The air
source heat pump cannot operate effectively and efficiently when snowbound just as a car cannot
function well in heavy snow conditions.

HEAT PUMP (Water-to-Air)

These types of heat pumps are also commonly referred to as water source or geothermal systems.
Just like the air source heat pump, they are refrigerant-based systems that both heats and cools using
a compressor for both modes of operation. The primary difference is that the system uses water or
antifreeze protected water solution instead of an air-cooled outdoor heat transfer coil, and there is no
outdoor motor/fan system but instead a water pump to provide adequate water flow to the system.
COOLING MODE
The cooling mode of a water-to-air heat pump is exactly the same as that described for an air
conditioner in the above section for Air Conditioners, except that the outdoor coil uses water instead
of air for the heat transfer medium.
HEAT PUMP (HEATING MODE)
The system operates in reverse cycle, meaning that it acquires and moves heat from the water
supply flowing through the water to refrigerant coil, and transfers it indoors to be rejected into the
circulating air stream.
Most water-to-air heat pumps (but not all) will also be equipped with some amount of electric heat
to supplement the heating capacity of the compressor system on an as needed basis. This operation
is entirely automatic and is controlled by the indoor thermostat.
Because of the design of water-to-air heat pumps and the water temperatures involved, no defrost
system is required as in air-to-air heat pumps.
WATER SUPPLY SYSTEMS
Depending upon type and application of the water-to-air heat pump, the water side of the system
could be one of the following:
1. Individual closed loop buried in a trench or vertical bore hole(s).
2. Individual loop submerged in a pond.
3. Water supplied from a well and discharged into pond, stream, ditch or another well.
4. Water supplied from a boiler/tower system, typically only in larger multi-unit installations.
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