Why are there so many different styles of heat pump?

Heat pumps are all the same, they are simple machines which all have to have a number of components without which they don’t work. 4 of the components are essential they are:

The compressor, it’s the refrigerant pump which does all the work.

The next part is the outdoor unit coil we use to harvest the free heat from the garden, we fridge engineers call it an evaporator, just to make life complex in air conditioning this same coil is called a condenser.

All units have a valve to control the refrigerant movement, its called an electronic expansion valve its basically an electronic version of the valve on your radiators (it will feature in a future blog)

And finally, we need a heat exchanger combining the hot refrigerant coil, or condenser and a water coil to take the heat away to heat the house. These are called plates, plate heat exchangers or HEX. They have refrigerant one side and water the other so technically we should call them refrigerant to water heat exchangers, they look like this.

There are 2 very distinct types of heat pumps:

A monobloc unit is defined as a unit which has all four of these refrigerant components above are housed in one box delivered to site as a complete system. Monobloc units are designed for heating engineers, who connect water pipework up to the unit outside, its simple just like a boiler but it lives in the garden. The advantage with Monoblocs is they are simple and any plumber can connect them up using their skills and tools, but pumping water up and down the garden is expensive, the pipes are large so they like to be installed close to the house.

A split unit is defined as a unit which does not have all four of the refrigerant components inside, the compressor, expansion valve and evaporator are in the box which lives outside , the refrigerant to water heat exchanger comes in another box which goes inside the house, SO the unit comes in two pieces which is why we call it a split. The two pieces are connected using refrigerant pipework, not water pipework.

Splits are designed for air-conditioning engineers. They are super popular in Southern Europe where the air conditioning engineers have no work in Winter, so they get involved in heating. A split unit needs both a heating engineer and a refrigeration or FGAS engineer to install them. The FGAs engineer installs the fridge pipework between the two boxes, the heating engineers connect water pipework up to the indoor unit, it looks exactly like a boiler so we give it a stupid name, we call it a hydro box. Splits have the advantage that its very easy to run refrigerant pipes long distances for a relatively low cost. Decent split units can go 75m down the garden with very little loss of heat. Neither is more efficient and neither is better.

?SO that’s the major classes explained, but its heat pumps so why not make it even more complex? In the water side of the system, we like:

an expansion vessel to take up the slack as the water cools and heats

A water pump to move the water round the house

And a flow switch which measures if the water is moving and if so, how fast.

A filter to keep all of the crap out of the heat exchanger, this would block it up,

Every heat pump on the planet needs all these bits. The only difference between the different heat pumps is where the manufacturers decide is best to place them.

The simplest units have none of these components inside, the plumber has to install them all him or herself somewhere in the house. Samsung and Mitsubishi do this. I call it self assembly.

Because this can be a pain to do on site manufacturers often screw all these bits on the front of the hot water cylinder to make the plumbers work easy, its called pre plumbing, or laziness.

Some monobloc units have these bits included inside the box in the garden, it makes them easier to install but physically bigger. Panasonic, Midea etc.

To make matters more complex there is a new breed of monobloc heat pump, you connect the water to the unit in the garden just like before, but the manufacturer puts all the plumbing components in a separate boiler shaped box inside the house. I call this a wet split. Brilliantly the indoor unit is also called a hydro box.

so basically that's it. The only major difference between the units is geography.

Hope you enjoyed this, I have a feeling it might be inside my second book 2 coming soon.