Heat Pumps use significantly more water flow than a boiler and are very sensitive to low water flow. The result of low water flow will be nuisance trips at best and damage to your heat pump at worst. For this reason we recommend using a thermal break.
What is a Thermal Break?
A thermal break is a device that separates the water heating circuit to and from the heat pump from the heat emitting circuit to and from the radiators. The heat pump heats the water which it circulates to and from the thermal break. The heating system takes heated water from the thermal break and circulates it to and from the heating system.
The first advantage is reliability. Since the heat pump always has full bore water flow then it cannot trip or be damaged by low water flow. It will continue to operate whatever happens in the heating circuit. Every single TRV could be shut down completely and the heat pump will carry on regardless. When we started selling heat pumps nuisance trips due to low water flow were common but since recommending thermal breaks they have become things of the past.
The second advantage is that a thermal break gives an end user piece of mind about who to call in the event of a problem. Typically a heat pump will be installed by a Renewables company while the heating system is looked after by a plumber or heating engineer. When there is a problem it is usual for each to blame the other and the householder does not know where to go! But with a thermal break it is absolutely clear cut. If there is a problem then the householder can go to the thermal break and see if it is warm. If it isn't then the heat pump is not operating for some reason and after checking that the heat pump is turned on and is receiving a demand from the heating controller and isn't producing hot water then they can check to see if a fault code is present on the system controller and call the Renewables company. But if there is a problem in the heating system and the thermal break is warm then it has to be a problem on the heating side and the householder can call the plumber or heating engineer.
The third advantage, if you use a buffer tank rather than a Low Loss Header, is that it gives you a thermal store of hot water to speed up the system reaction time and allow the heating system to carry on working when the heat pump is generating domestic hot water.
The fourth advantage is that a thermal break allows more complex types of heating system such as bivalent systems with several source of heating possible. Combining multiple heat pumps, a heat pump and a boiler or similar is easy using a thermal break.
We very strongly recommend the use of a thermal break in all heat pump heating systems!
Low Loss Headers
A low loss header is suitable for most heat pump applications and is much smaller and quicker to respond to demand than a buffer tank.
It consists of a small water reservoir, typically of one or two litres, with a boiler flow and return connection on one side and a heating flow and return connection on the other. At the top is an automatic air vent and at the bottom is a drain point.
We have a fantastic range of low loss headers suitable for a wide range of capacities. They are pre insulated and have pockets for temperature sensors or thermostats as standard. We can also supply manifolds for two, three or more heating circuits. We can also supply pump sets for connection to these manifolds. They are all high quality and very reasonably priced.
A low loss header and a low loss header with a two way manifold are shown above. The manifold is used when you have two or more heating circuits.
The low loss header above is connected to a manifold with three heating circuits. Each has its own pump and isolating valves plus a return strainer. Each one also has a flow and return thermostat to give a visual indication of the flow and return temperature in that part of the circuit.
From left to right firstly we have a basic pump set suitable for a heating circuit which will have full bore flow all of the time such as a fan coil circuit. A fan coils uses a valve which will either pass the water through the fan coil or bypass it and so never interrupts the water flow like a TRV does.
In the middle we have an under floor heating pump set with an additional water mixing valve. The mixing valve ensures that the water does not exceed the design temperature for the under floor heating circuit.
On the right we have a radiator pump set with a differential pressure regulating valve to bypass water from the return to the flow side as the TRVs start to shut down. We also have a regulating valve to regulate the hot water flow temperature but we would not usually use this valve with a heat pump system as the heat pump controls the flow temperature.
These manifold and pump sets are a good way to save time on site as well as ensuring that the system operates correctly. We would be glad to give you a quote.
These are similar to a low loss header but are much larger and act as a water storage device as well. Typically you might use a tank rather than a header where the water circuit is below the 50 litre minimum for an Aquarea system.
They can also give a reservoir of hot water for heating to enable the radiators to stay warm when the heat pump is generating domestic hot water. Typically a 200 litre buffer tank will give around eight minutes of water with a 9KW heat pump, meaning that in eight minutes it will have reduced in temperature by 5C., in sixteen minutes by 10C and in half an hour by 20C.
We would not normally fit a boost electric heater to a buffer tank but could easily do so. Another option would be to mount an external electric boiler for boost heating.
If the total system water quantity, including the buffer tank, will exceed 200 litres then you will need an additional expansion vessel.
Typically we would use a buffer tank containing around four or five minutes worth of water so for a small 6 KW system then an 80 litre model would be fine.
The pump in the Aquarea system will pump water between itself and the thermal break. A pump, or pumps, must be fitted after the thermal break in order to send water to and from the heating system. We recommend that each heating circuit has its own circulation pump and you should ensure that this is large enough to move the quantity of water required.
Tip - Typically having a small pump in the flow and also one in the return is more cost effective than one single larger pump.