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An air-to-air/water heat pump uses the ambient temperature of the outside air.


Pro:
- Easy installation
- Low initial cost

Contra:
- Available energy is depending on the temperature of the outside air.
(at its lowest when the outside air temperature is low)
- Defrosting of the evaporator is needed at lower outside air temperatures

Air-to-air/water heat pump

Air-to-air heat pumps

Two different distribution mediums

work using outdoor air as the source and indoor air as the distribution medium
Between the outdoor unit and indoor unit you find refrigerant lines

Air-to-water heat pumps
(split)

Air-to-water heat pumps

(monobloc)

work using outdoor air as the heat source and water as the distribution medium (feeding underfloor heating or radiators)
Between the outdoor unit and indoor unit you find refrigerant lines

work using outdoor air as the heat source and water as the distribution medium
(feeding underfloor heating or radiators)
The monobloc unit (outside unit) is directly connected to the water of the heating system.

Air-to-air heat pump

An air-to-air heat pump has the same components as a normal airconditioning unit for cooling, but its main focus is heating instead of cooling.


The temperature is adjusted by a remote control, which gives an infrared signal to the indoor unit (IDU).

The indoor unit warm up the air in the room with the heat that is in condensor.
Between the condesor and the evaporator (located in the outdoor unit ODU), there are refrigerant lines filled with a refrigerant.
This setup can be found in a split or multisplit setup.

This setup doesn't allow production of domestic hot water.

Air-to-water heat pump (split)

An air-to-water heat pump (split) uses the same concept as a air-to-air heat pump, but instead directly transmitting the heat from the condensor to the air in the room it transmits the heat to another distribution medium, water.


This water is then pumped around in the heating circuit and feeding radiators, convectors or underfloor heating.
Because a heat pump is a low temperature heat generating device, the heat transmitting options should also be low temperature (max 55°C).
[There are exceptions, but not dominant on the market]

Additional hot water production with the heat pump is available.

Air-to-water heat pump (split)

Build-up of a air-to-water heat pump:


- Outdoor unit
- Indoor unit
- Buffer boiler for heating
- Domestic hot water tank for hot water
- Heat transmitting devices (Underfloor heating / radiators)







(Click on the interactive elements to discover the details)

Split heat pumps outdoor units are placed outside next to the house. They are generally smaller than their monobloc counterparts because the condenser is inside the building.



The lower the temperature of the heat transmitting device, the better. But radiators can still work together with a heat pump.

The flow temperature for radiators will be limited to < 55°C, thus in a renovation a heat loss calculation and check of the size of the radiator is needed.


Heat pumps on a higher temperature are generally less efficient (efficiency loss of ~66%)


Other options like convectors specific for heat pumps (low temperature) can also be used.

Underfloor, wall, ceiling heating are very suited for heat pumps due to the low flow temperature that they use to heat up a room.


New underfloor heating systems are planned with a flow temperature of ~35°C, where older systems go up to ~55°C


Underfloor heating example






Domestic hot water (DHW) boilers can be used together with a heat pump to produce hot water.

Because a heat pump works with lower flow temperatures, these DHW boilers are usually bigger than their counterparts combined with fossil fuel sources.

Domestic hot water boiler for a heat pump


Heat pumps are very often combined with a buffer boiler for heating.

This buffer boiler allows longer running times for the heat pump, due to a higher available water volume in the heating system.

Older heat pumps don't have the ability to modulate their heating power, in this case buffer boilers are needed.

New generation heat pumps can modulate, but it is still advised to use a minimal amount of buffer.


Rule of thumb is= 20l/kW calculated on the power of the heat pump (with modulating system you could theoretically use the lowest modulation point)

eg. 7 kW (heat pump) x 20l/kW = 140 Ltr. buffer boiler

A buffer boiler is nothing more than a big tank with water in it

In the future a buffer boiler can also be used to store heat for when it is needed and detach production from usage.

eg. Agile heating, only activate the heat pump when there is a lot of production of renewable energy.





Indoor unit have a condenser inside which connects the refrigerant to the water.

Typically they look like a gas condensing boiler from the outside (minus the exhaust pipe)


Indoor unit of a split heat pump



Air-to-water heat pump (monobloc)

An air-to-water heat pump (monobloc) differs from the split option by including the whole vapour compression cycle in the outdoor unit (ODU).

This means that between the unit outside and the heat transmitting options inside there is just water.
The installation of these kind of heat pumps don't need a cooling technician and are focused on the heating installer.

Typically the monobloc heat pumps are bigger than their split counterparts.

Air-to-water heat pump (monobloc)

Build-up of a air-to-water heat pump:


- Monobloc heat pump
- Buffer boiler for heating
- Domestic hot water tank for hot water
- Heat transmitting devices (Underfloor heating / radiators)








(Click on the interactive elements to discover the details)

Monobloc heat pump are placed next to the house (inside variants are also available), they are usually smaller than their split counterparts.

The lower the temperature of the heat transmitting device, the better. But radiators can still work together with a heat pump.

The flow temperature for radiators will be limited to < 55°C, thus in a renovation a heat loss calculation and check of the size of the radiator is needed.


Heat pumps on a higher temperature are generally less efficient (efficiency loss of ~66%)


Other options like convectors specific for heat pumps (low temperature) can also be used.

Underfloor, wall, ceiling heating are very suited for heat pumps due to the low flow temperature that they use to heat up a room.


New underfloor heating systems are planned with a flow temperature of ~35°C, where older systems go up to ~55°C


Underfloor heating example






Domestic hot water (DHW) boilers can be used together with a heat pump to produce hot water.

Because a heat pump works with lower flow temperatures, these DHW boilers are usually bigger than their counterparts combined with fossil fuel sources.

Domestic hot water boiler for a heat pump


Heat pumps are very often combined with a buffer boiler for heating.

This buffer boiler allows longer running times for the heat pump, due to a higher available water volume in the heating system.

Older heat pumps don't have the ability to modulate their heating power, in this case buffer boilers are needed.

New generation heat pumps can modulate, but it is still advised to use a minimal amount of buffer.


Rule of thumb is= 20l/kW calculated on the power of the heat pump (with modulating system you could theoretically use the lowest modulation point)

eg. 7 kW (heat pump) x 20l/kW = 140 Ltr. buffer boiler

A buffer boiler is nothing more than a big tank with water in it

In the future a buffer boiler can also be used to store heat for when it is needed and detach production from usage.

eg. Agile heating, only activate the heat pump when there is a lot of production of renewable energy.





Ground-to-water heat pump

An ground-to-water heat pump uses temperature of the ground. Either with a horizontal or a vertical ground coupled system.


Pro:
- Available energy is more stable as the temperature in the ground is more stable.
- High COP / SPF

Contra:
- High investment cost due to the drilling or digging.
- For a horizontal ground coupled system, big surface is needed (1,5x to 2x the heating surface)
- For a vertical ground coupled system, approval for drilling is needed

Ground-to-water heat pump

Ground-to-water heat pump

Build-up of a ground-to-water heat pump:


- Ground source heat pump
- Network of pipes
- Buffer boiler for heating
- Domestic hot water tank for hot water
- Heat transmitting devices (Underfloor heating / radiators)







(Click on the interactive elements to discover the details)

With the ground-to-water heat pump we take energy from the ground with a piping network.

In this example there is a horizontal piping network, this is placed approx 1m under the ground in trenches.

The lower the temperature of the heat transmitting device, the better. But radiators can still work together with a heat pump.

The flow temperature for radiators will be limited to < 55°C, thus in a renovation a heat loss calculation and check of the size of the radiator is needed.


Heat pumps on a higher temperature are generally less efficient (efficiency loss of ~66%)


Other options like convectors specific for heat pumps (low temperature) can also be used.

Underfloor, wall, ceiling heating are very suited for heat pumps due to the low flow temperature that they use to heat up a room.


New underfloor heating systems are planned with a flow temperature of ~35°C, where older systems go up to ~55°C


Underfloor heating example






Domestic hot water (DHW) boilers can be used together with a heat pump to produce hot water.

Because a heat pump works with lower flow temperatures, these DHW boilers are usually bigger than their counterparts combined with fossil fuel sources.

Domestic hot water boiler for a heat pump


Heat pumps are very often combined with a buffer boiler for heating.

This buffer boiler allows longer running times for the heat pump, due to a higher available water volume in the heating system.

Older heat pumps don't have the ability to modulate their heating power, in this case buffer boilers are needed.

New generation heat pumps can modulate, but it is still advised to use a minimal amount of buffer.


Rule of thumb is= 20l/kW calculated on the power of the heat pump (with modulating system you could theoretically use the lowest modulation point)

eg. 7 kW (heat pump) x 20l/kW = 140 Ltr. buffer boiler

A buffer boiler is nothing more than a big tank with water in it

In the future a buffer boiler can also be used to store heat for when it is needed and detach production from usage.

eg. Agile heating, only activate the heat pump when there is a lot of production of renewable energy.





Ground to water heat pumps are located in the technical area (normally close to the buffer and domestic hot water boiler)






Ground-to-water heat pump

Build-up of a ground-to-water heat pump:


- Ground source heat pump
- Several vertical drillings
- Buffer boiler for heating
- Domestic hot water tank for hot water
- Heat transmitting devices (Underfloor heating / radiators)







(Click on the interactive elements to discover the details)

With the ground-to-water heat pump we take energy from the ground with a piping network.

In this example there is a vertical piping network.

Vertical drilling is more expensive, but provides a more solid temperature over the year.



The lower the temperature of the heat transmitting device, the better. But radiators can still work together with a heat pump.

The flow temperature for radiators will be limited to < 55°C, thus in a renovation a heat loss calculation and check of the size of the radiator is needed.


Heat pumps on a higher temperature are generally less efficient (efficiency loss of ~66%)


Other options like convectors specific for heat pumps (low temperature) can also be used.

Underfloor, wall, ceiling heating are very suited for heat pumps due to the low flow temperature that they use to heat up a room.


New underfloor heating systems are planned with a flow temperature of ~35°C, where older systems go up to ~55°C


Underfloor heating example






Domestic hot water (DHW) boilers can be used together with a heat pump to produce hot water.

Because a heat pump works with lower flow temperatures, these DHW boilers are usually bigger than their counterparts combined with fossil fuel sources.

Domestic hot water boiler for a heat pump


Heat pumps are very often combined with a buffer boiler for heating.

This buffer boiler allows longer running times for the heat pump, due to a higher available water volume in the heating system.

Older heat pumps don't have the ability to modulate their heating power, in this case buffer boilers are needed.

New generation heat pumps can modulate, but it is still advised to use a minimal amount of buffer.


Rule of thumb is= 20l/kW calculated on the power of the heat pump (with modulating system you could theoretically use the lowest modulation point)

eg. 7 kW (heat pump) x 20l/kW = 140 Ltr. buffer boiler

A buffer boiler is nothing more than a big tank with water in it

In the future a buffer boiler can also be used to store heat for when it is needed and detach production from usage.

eg. Agile heating, only activate the heat pump when there is a lot of production of renewable energy.





Ground to water heat pumps are located in the technical area (normally close to the buffer and domestic hot water boiler)






Water-to-water heat pump

An water-to-water heat pump uses temperature of a water source.


Pro:
- Available energy is more stable as the temperature of the ground water is
- High COP / SPF

Contra:
- High investment cost due to the drilling
- Approval of authorities is needed for use of water source (environmental regulations)

Water-to-water heat pump

Ground-to-water heat pump

Build-up of a ground-to-water heat pump:


- Ground source heat pump
- Several vertical drillings
- Buffer boiler for heating
- Domestic hot water tank for hot water
- Heat transmitting devices (Underfloor heating / radiators)







(Click on the interactive elements to discover the details)

With the water-to-water heat pump we take energy from a ground water source with a piping networ (open or closed)

The lower the temperature of the heat transmitting device, the better. But radiators can still work together with a heat pump.

The flow temperature for radiators will be limited to < 55°C, thus in a renovation a heat loss calculation and check of the size of the radiator is needed.


Heat pumps on a higher temperature are generally less efficient (efficiency loss of ~66%)


Other options like convectors specific for heat pumps (low temperature) can also be used.

Underfloor, wall, ceiling heating are very suited for heat pumps due to the low flow temperature that they use to heat up a room.


New underfloor heating systems are planned with a flow temperature of ~35°C, where older systems go up to ~55°C


Underfloor heating example






Domestic hot water (DHW) boilers can be used together with a heat pump to produce hot water.

Because a heat pump works with lower flow temperatures, these DHW boilers are usually bigger than their counterparts combined with fossil fuel sources.

Domestic hot water boiler for a heat pump


Heat pumps are very often combined with a buffer boiler for heating.

This buffer boiler allows longer running times for the heat pump, due to a higher available water volume in the heating system.

Older heat pumps don't have the ability to modulate their heating power, in this case buffer boilers are needed.

New generation heat pumps can modulate, but it is still advised to use a minimal amount of buffer.


Rule of thumb is= 20l/kW calculated on the power of the heat pump (with modulating system you could theoretically use the lowest modulation point)

eg. 7 kW (heat pump) x 20l/kW = 140 Ltr. buffer boiler

A buffer boiler is nothing more than a big tank with water in it

In the future a buffer boiler can also be used to store heat for when it is needed and detach production from usage.

eg. Agile heating, only activate the heat pump when there is a lot of production of renewable energy.





Water to water heat pumps are located in the technical area (normally close to the buffer and domestic hot water boiler)

They are mainly the same heat pumps as their ground-to-water counterparts, but come with an additional heat exchanger to split the water of the heat pump and ground water






Working principles of a heat pump

Monovalent

Bivalent-parallel

Bivalent-alternative

Bivalent-partially parallel

Heat pumps can be implemented differently, these are the four (five) working principles.


- Monovalent
- Bivalent-parallel (mono-energetic)
- Bivalent-alternative
- BIvaent-partially alternative

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In monovalent operation the heat pump works completely independent from an additional heat source.

The heat pump covers 100% the heat loss of the building.

Bivalent-parallel operation means that the heat pump works together with an additional heater when the heat pump reaches a certain point that it can't cover the heat loss of the building.


If this additional heater is an electrical resistance this is also called mono-energetic (because there is no other source than electricity)

Bivalent-alternative means that the heat pump works together with an auxiliary heater when the heat pump reaches a certain point that it can't cover the heat loss of the building.

It switches off the heat pump completely and everything below the bivalent point is heated up by the auxiliary heater

Bivalent-partially parallel means the heat pump works alone above the switching temperature. Heat pump and auxiliary heating work simultaneously for ambient temperatures between the switching temperature and the switch-off temperature.

Bivalent point

For air-to-water heat pumps, at a low air temperature, the heat pump becomes less efficient and needs an additional heater to cover the heat loss of the building.

The moment the additional heater needs to be activated is the bivalent point.

In practice this bivalent point is around -10 to -5°C.
This means that only a short amount of time during the year, an addtional heater needs to help out. (gray area)

This additional heater can be an electrical resistance already inside the heat pump (mono-energetic) or this can be a heating boiler.

The latter is called a hybrid system

The bivalent point is determined with the characteristics of the heat pump in corelation with the calculated heat loss and the standard outside temperature.


eg.


Heat loss building (DIN EN 12831) Qtotal = 8 kW

Standard outside temperature (Munich) = -15°C

Heat pump = Vitocal 200-s


Bivalent point = -8°C

Needed power additional heater= 3 kW








Hybrid systems

Due to technical limitations, the combination of heat pumps with heating boilers is done.

Either to achieve higher flow temperatures or easier integrations of a heat pump system.

A lot of different constellations are possible, the example in the image on the side is a simplified example.

To achieve a good hybrid system, the heat pump controller should be in charge of the bivalent point.