Hydronic Heat Pumps and Air Conditioners

Hydronic heat pumps and air conditioners are similar. An air conditioner is in fact a heat pump in reverse cycle. Also, a hydronic heat pump can provide air conditioned cooling in summer. Whilst both can provide heating and cooling, it is fair to say that hydronic heat pumps are better at heating whilst air conditioners are better at cooling.

Hydronic heat pumps use water to transfer heat from outside to inside in winter and from inside to outside in summer.  Air conditioners do this using air to transfer the heat. However, water enables superior radiant heating through underfloor hydronic circuits or radiator panels. Hydronic heat pumps can also provide chilled water cooling using fan coil convectors. This works similarly to indoor units of air conditioning systems, except instead of chilled refrigerant flowing through indoor unit coils in summer, it is chilled water. Also, plumbing water lines for your hydronic heating and cooling system may also be easier.

Try holding your finger over a bicycle pump, the air (gas) gets very hot. This is what happens when you compress refrigerant after it has turned into a gas. The really useful thing about refrigerant used in most hydronic heat pumps is that it boils into a gas at minus 48 deg C. Therefore, it can extract ”heat” from outside air well below zero. This makes air sourced heat pumps ideal for southern and inland Australian climates.

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Schematic of Ducted Air Conditioning system.

In the Australian winter, reverse cycle air conditioners and heat pumps nearly always source their heat from the outside air. However, they can also source heat from water such as a river, lake, sea or even effluent pipes. Heat can be sourced from underground but this is expensive and may only be cost effective in Alpine areas. In summer, they remove heat from inside and transfer that heat outside.

The heat source for hydronic heating can also be a gas boiler but this will only heat and not cool. However, hydronic heat pumps heat and cool in reverse cycle.

Air conditioners are more effective at cooling because air movement assists the cooling process. Heat pumps are more effective at heating because radiant heat is more efficient and also more comfortable than heat blown from an indoor unit.

Schematic showing an underfloor hydronic heating and cooling system with a heat pump.

The use of water by hydronic heat pumps to transfer heat is very efficient because water is 3,300 times more effective at transferring heat than air. This is why hydronic heat pumps only need small water pipes for underfloor hydronic circuits or radiators. On the other hand, ducted air conditioners need large air ducts for heating and cooling.

Consider investing in a hydronic heat pump system at least in the rooms where your family life is based. To save money, install air conditioning in your bedrooms. This approach works better if you have a two storey home with bedrooms on the first floor. This is because warm air from your hydronic heat pump system rises in winter and cold air from your air conditioner falls in summer. Also, your air conditioning system will manage humidity levels for the whole house.

Here are some ways to improve the performance of your heating & cooling systems:

  • Clean the filters of your equipment regularly, at least prior to each heating and cooling season.
  • Adjust your inside set temperature up and down with the seasons. This also improves your ability to adapt to changing weather.
  • Install ceiling fans to reduce the effective temperature you feel by around 4 degrees in summer. Then you can raise the set temperature.
  • Zone off some rooms so you don’t need to heat or cool your whole house all the time.
  • Consider heat recovery ventilation to reduce the need for opening windows.

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