Water is Better than Air as a cooling medium
Water is 784 times denser than air and has 4.23 times the heat carrying capacity than air. Therefore, water is approximately 3,300 (784 x 4.23) more effective as a heating/cooling medium than air. This is why hydronic heating/cooling is so effective. Also, for a heat pump, running the water out at moderate heating and cooling temperatures is easy which makes the efficiency of modern inverter heat pumps very high. In fact, the heating or cooling is typically more than 4 times the power input. If this power can be generated by your own solar panels, then you have a very efficient heating and cooling system that costs little or nothing to operate.
Hydronic Passive Cooling for Homes
If you use a heat pump for Hydronic heating, you can reverse the cycle in summer to send cold water (above the dew point) through your hydronic underfloor circuits or radiators. This provides a passive cooling effect that absorbs heat from the air (does not radiate cooling) and takes this energy away to the heat pump to be cooled.
Passive cooling works best:
- In Australian climates south or inland where humidity is lower
- With underfloor heating/cooling circuits in-slab or in-screed due to the large surface area available for optimal heat transfer
- By removing the heat bank effect from sunshine coming through windows radiating and heating the floor slab
- With gentle air movement from fans to aid the heat transfer, moving the heat across the floor. Ceiling fans are best because they will push down the warm rising air to be absorbed into the cool floor and they also provide a cooling effect as well through convection by moving air across your body making you feel several degrees cooler.
- With large air volume from high ceilings because you do not have to heat cool the whole air space to be effective at floor level.
Hydronic Cooling with Radiators
Hydronic radiators also provide a cooling effect but to a lesser extent due to less surface area. Radiators are primarily designed for heating. Some people choose to combine air conditioning with radiators and in this case the air conditioner can be used in fan cycle to move air across the cool radiators to enhance the cooling effect. This may well be sufficient for most of the summer apart from the heat waves. It depends on your comfort levels, house design, insulation levels and location. You may like to trial the effectiveness of radiator cooling for one summer and then decide if you need an air conditioner to provide a cooling boost on very hot days next summer.
The most luxuriant form of heating / cooling
Hydronic heating / cooling is the most luxuriant form of heating / cooling and certainly best for people with asthma, so investing in this makes good sense for your living and family rooms, where you spend most of your indoor time awake. Some people choose a combined approach to reduce heating and cooling installation costs and use reverse cycle air conditioning in bedrooms with hydronic heating/cooling in living rooms. If bedrooms are cool prior to bedtime, then you may not need additional cooling through the night (depending on the night time air temperature and your personal comfort levels). If some additional night time cooling is required, fans may be all that is needed. On heat wave nights, air conditioning may provide a cooling boost.
Floor Coverings for Hydronic Heating / Cooling
Underfloor hydronic heating radiates heat from the floor at a gentle 26°C and underfloor cooling absorbs heat from the air at a comfortable 18 deg C under foot. It works well with almost any floor surface except softwood and bamboo floor boards. Underfloor heating works best with hard surfaces like polished concrete, tiles, plastics and engineered hardwood boards (https://www.havwoods.com.au/). It can also work effectively with loose weave carpets with resistance of less than 0.15 m2K/W.
Other benefits of Hydronic Heating / Cooling
Apart from the efficiency and luxuriant feel of hydronic heating/cooling, other benefits include:
- Better for people with an asthma condition
- Does not take up wall space for home furnishing
- Is ubiquitous, and you don’t know its there apart from the luxuriant feel
- Makes no noise
- Allows for fine climate control and room zoning
- Doesn’t need to heat or cool the air volume at ceiling height to feel comfortable at floor level
- No need for duct work, ceiling diffusers or indoor wall units
- Ideal for high cathedral ceilings with insufficient room to run air conditioning ducting
- Preserves the humidity in the air so you don’t get overly dry air
For air to feel good, we don’t want it to be too dry as in planes and not too humid as in tropical climates, we want the ‘’goldilocks’’ level in between. The heat pump should have a dew point monitor to ensure the cooling temperature stays above the dew point, which will vary with the ambient air humidity through the summer. If high humidity may sometimes be a problem, then hydronic cooling can be combined with a hydronic fan coil or dehumidifier to reduce the humidity to the comfortable ‘’goldilocks’’ level’’.