A common question posed by many clients, many consumers are led down the route by their installer or their own desire not to have a buffer tank “as it can take up too much space”. As a result it is important to understand what is a buffer tank, the impact a buffer tank has on a heat pump system, what will happen if you don’t have one and which heat pumps don’t need one.
What is a Buffer Tank?
A buffer is in simple terms, a tank that contains a certain amount of water. This water increases the volume of the heating distribution system. During the low load conditions, the extra volume of water would absorb any of the extra heat generated by the heat pump.
Do I need a buffer tank?
A buffer tank is a volume of water that can assist the consumer in reducing the amount of time the heat pump has to ‘cycle’. A buffer tank would be necessary in a larger domestic property or commercial project where there may be many heating zones required. However, in houses that are either open-plan or well insulated, a large buffer tank may not be a necessity. In well insulated properties, floor with sufficient pipe and good thermal conduct can actually act as the buffer. In houses with high water content radiators, they can also act as a buffer.
When considering if a buffer tank is absolutely necessary, it would be essential to consider the size of the heat pump. If the heat pump is particularly large, it is likely that instead of a continuously-running small buffer tank, you will require a buffer cylinder. In some cases an air source heat pump (ASHP) will not have variable ‘inverter’ motors. These motors modulate the output of the pump and they therefore, would not require a buffer cylinder. However, with fixed speed air source the heat output often varies and this depends on the temperature of the outside air. In this case a buffer tank would definitely be recommended. Both the size and the operating temperature of the buffer tank will affect the efficiency and effectiveness of the tank.
What if I don’t fit a buffer tank?
Greater number of cycles: your heat pump will turn on and off a greater number of times. This reduces the life expectancy of the compressor and uses more energy to start the motor. As a result this leads to higher service and running costs.
Less heating control: to prevent the heat pump from cycle-ing too often, some installers remove or reduce the number of thermostats. As a result the property effectively becomes the buffer, the property owner has less control over the system. This will result in significantly higher running costs and is a wasteful method of running your system. Without a buffer tank you cannot have individual room control.
No control over running costs: without room stats the only thing that is then controlling the on/off of your heating system is the clock, not the heating requirement of the rooms.