Part 5: How to select the right air source heat pump and why?

Following on from part four of the series, where Chris Higgs took a closer look at refrigerant types for heat pumps, here, Chris considers what we mean by ‘split’ and ‘mono’ heat pumps, and how you can help your customer to decide which one is right for them.

Split or Mono

What do we mean when we say ‘split’ or ‘mono’? A split heat pump is one in which the outdoor unit (which contains the compressor) is connected to the indoor unit (which contains the condenser) via refrigerant filled pipework. The flow and return pipework for the heating system / hot water circuit are attached to the indoor unit in this setup. By contrast, a mono or monoblock heat pump is one in which the full refrigerant circuit is hermetically sealed and housed in the outdoor unit. The only thing which comes out of the back of the monoblock heat pump is heated water for the heating and/or hot water circuit. How do you decide which heat pump type to use? In our experience, there are two main deciding factors which help determine whether a split or monoblock heat pump is the right choice for the project. Those factors are distance and temperature. By distance, we mean the distance from the property to where the heat pump is to be located. If the heat pump is to be installed right next to the property, then a monoblock heat pump will suffice. At anything more than 10 metres, for a standard domestic install, we would tend to advise going for a split heat pump, as the price for pre-insulated pipework suitable for heated water, and the ground works involved can become prohibitive above around 10 metres.

When we talk about temperature, we talk about the flow temperature available from the heat pump. As discussed in more detail earlier on, in the main, monoblock heat pumps can achieve sustained flow temperatures up to 60 to 65°C (perfect for underfloor through to

radiators), whereas traditionally a split heat pump would be required to provide the 80°C flow temperature that an older retrofit property may require.

Compact Mono or “True” Monoblock

So, what do we mean by compact or ‘true’ monoblock? A compact by our (and much of the industry) definition is a monoblock heat pump where the primary circulation pump (the one that gets the heated water from the heat pump into the house), and expansion vessel are not located inside the heat pump and so need to be installed in the property. In some cases, a compact mono heat pump may also have a wiring centre and controller located in the property. An example of a compact mono air source heat pump would be the Mitsubishi Ecodan mono or Samsung GEN6 EHS Mono.

The cousin of the compact mono is the ‘true’ monoblock. A ‘true’ monoblock heat pump, is, in essence, an all-in-one monoblock unit. Classically, you would find inside the outdoor unit, at least, an expansion vessel and primary circulation pump. On many ‘true’ monoblock units, you can also find what you may call the indoor PCB or wiring centre meaning that 2 port valves and room thermostats will wire to the outdoor unit. A very good example of a “true” monoblock would be the Midea MHC range, as a single box arrives with circulation pump, expansion vessel, PRV and auto air vent contained inside the unit with inline strainer, domestic hot water sensor cable and remote controller as loose components, but still inside the one box.

We hope this helps you to help your customers choose the right heat pump for them. Join us for the sixth and final part in our series, where Chris Higgs considers the cost of heat pumps and why accreditation, such as that from MCS, is important for installers.