4
2. Intended Use of the System M Heat Pump
2.1 Area of Application
2.2 Operating Principle
The air-to-water heat pump is to be used exclusively for heating or cooling of
HVAC system distribution water and indirect domestic hot water production.
It can be used in new or existing home comfort (HVAC) systems.
The heat pump is suitable for mono energy and bivalent operation in outside
air temperatures down to -7 °F (-22 °C).
Mono energy operation
The heat pump alone supplies a large part of the required heat output. On
the few days during the year with extremely low outdoor temperatures (<
20 °F, -7 °C), the supplied buffer tank immersion heater can supplement
the heat pump. Both heat generators are operated with one type of
energy (electricity), e.g. mono energy. This operating mode is a sensible
choice if air serves as the heat distribution source, since raising the
number of hours per year during which the heat pump is operated to its
full potential does not require changes to the heat distribution system.
Experience has shown that in air-to-water heat pump heating systems,
more than 95% of the annual energy demand can be provided by the
heat pump alone.
Bivalent operation
The heat pump alone covers most of the heat consumption. In the event
of very low outdoor temperatures, the heat pump is supplemented by a
second heat generator, e.g. fossil-fuel fired boiler. This operating mode
is mainly used when old buildings are renovated and the existing boiler
is to be kept in use.
Proper defrosting of the heat pump evaporator is guaranteed by maintaining
a heating water return temperature from the heat pump to the HydroBox of
more than 68 °F (20 °C) during continuous operation.
It is not designed for the increased heat consumption required when a
building is being dried out. For this reason, the additional heat consumption
should be met using special devices provided by the customer.
In cooling operation, the heat pump is suitable for air temperatures ranging
from 55 °F to 113 °F (+12.8 °C to + 45 °C). It can be used for dynamic (fan
assisted) cooling. The minimum water temperature is 45 °F (+7 °C).
Heating
Surrounding air is drawn in by the heat pump's fan and fed through the
evaporator (heat exchanger). The evaporator cools the air, i.e. extracts
heat from it. This extracted heat is then transferred to the working medium
(refrigerant) in the evaporator.
The heat is "pumped" to a higher temperature level by increasing its pressure
with the aid of the electrically driven compressors. It is then transferred to
the heating water via the liquefier (heat exchanger).
Electrical energy is used to raise the temperature level of the heat from the
environment. Because the energy extracted from the air is transferred to
the heating water, this type of device is referred to as an air-to-water heat
pump.
The heated water is transferred to the indoor unit's buffer tank by the
integrated variable speed heat pump circulating pump (M16). The buffer
tank provides storage volume for supply out to the HVAC system.
The main components of the air-to-water heat pump consists of the
evaporator, fan and expansion valve, as well as the compressors, the
liquefier and the electrical control system. (See Fig 1)
At low ambient temperatures, humidity accumulates on the evaporator
in the form of frost, reducing the transfer of heat. Uneven accumulation
during this process does not indicate a fault. The evaporator is defrosted
automatically by the heat pump as required. Under certain atmospheric
conditions, steam may be emitted from the air outlet.
Cooling
The functions of the evaporator and the liquefier are reversed in the
"Cooling" operating mode.
The heating water transfers its heat to the refrigerant via the liquefier,
which is now functioning as an evaporator. The refrigerant is brought to a
higher temperature level using the compressor. Heat is transferred to the
surrounding air via the liquefier (which, in heating operation, functions as
an evaporator).
The chilled water is transferred to the indoor unit's buffer tank by the
integrated variable speed heat pump circulating pump (M16). The buffer
tank provides storage volume for supply out to the HVAC system.
Domestic Hot Water
Heated water is also transferred, when required, from the heat pump directly
to the indirect domestic hot water (DHW) tank by the integrated variable
speed DHW tank circulating pump (M18), bypassing the buffer tank.
This direct supply provides for a quicker response when domestic hot water
is required and quicker return to cooling once the DHW call is completed, as
the buffer tank can remain full of chilled water. Domestic hot water always
has priority.
