Heat pump thermal battery maximises your solar power

Thermal Battery
Heat Pump Hydronic Buffer Tanks, 100 up to 1500 litres

Consider adding a larger heat pump thermal battery (buffer tank) to your heat pump hydronic heating and cooling system. 

This will increase the internal mass of your home for greater thermal storage.

Therefore, your home will benefit in these ways:

  • Moderates the extremes of your indoor temperature range
  • Stabilizes your indoor temperature
  • Balances the temperature better throughout your home
  • Reduces your energy consumption due to the passive warming and cooling effect
  • Maximises your solar power during the day
  • Particularly beneficial in a southern or inland Australian climate

Thermal mass is particularly beneficial in climates with high diurnal variation, where there is a large difference between the day and night time temperatures. This is particularly important in southern and inland Australian climates which have this high diurnal variation. Ideally, your home should be constructed with high thermal mass inside the building fabric such as a concrete slab or feature walls made of brick or stone.

If your home is made of lightweight construction, such as timber framed weatherboard on suspended floor, then you should consider adding thermal mass.

If you are considering installing a heat pump hydronic system, you have the opportunity to add thermal mass by installing a large buffer tank. This is a heat pump thermal battery. A heat pump has the added benefit over a gas boiler in that it can reverse cycle and provide cooling in summer. It can also be powered by your solar panels during the day.

Water is a very good store of thermal energy so increasing the size of the buffer tank is a good way to add thermal mass. You can look at this as a thermal battery. Your heat pump hydronic system needs a buffer tank to operate efficiently and effectively. However, you can increase your buffer tank size to 200, 400, 700 or even up to 1500 litres to create a very large thermal battery.

In summer, your thermal battery works to keep your home cooler. When the temperature rises during the day, your heat pump can operate in reverse cycle removing heat from your inside your home and transferring it outside. This works better with underfloor hydronic systems due to the large surface area. Hydronic radiators in reverse cycle will provide some cooling but are less effective due to lower surface area. Fan convectors such as in-floor trench and concealed types are better because they draw air across the cold-water coils. For more information: heat pump hydronic heating

If you are installing solar panels, then adding thermal mass is a more important consideration. This is because your daytime solar power can be stored in the thermal battery of your buffer tank and building mass for release into the evening. The thermal energy stored will moderate the change of temperature in the evening when you are no longer producing solar power. For more information: solar power your home

To give an idea of how much solar power you need to run a heat pump, an 8.5kW Stiebel Eltron heat pump can heat and cool a home of around 150m2. This heat pump will need 1.8kW of power for underfloor heating with an outside air temperature of 7 degrees. It will need slightly more power below this temperature and less above. Radiator heating will need a bit more power because the water temperature needs to be higher than underfloor heating.

A 14kW Stiebel Eltron heat pump can heat and cool a home of around 250m2. This heat pump will need 2.9kW of power for underfloor heating with an outside air temperature of 7 degrees. Also, the same variations occur as in the above example. For more information: Stiebel Eltron hydronic heat pump

Your solar system should be sized well above 1.8 or 2.9kW to provide for other appliances and rainy and overcast days. Your solar panels will produce the power quoted only in ideal conditions when the sun is shining at a perpendicular angle to your panels. Your fridge will need around 1kW of power when it operates and your oven and microwave around 2kW. For more information: managing your solar power