Heat Pump technology is being used in one of the most common appliances in our homes – the fridge. The principle of a heat pump is to move energy by the means of electricity, refrigerant gas and compressor and it can do both HEATING and COOLING. We are extracting it from a warmer ambient i.e. the food in the fridge; and dumping it, this process is called COOLING. Or harvesting energy from the air outside our homes and passing it to the air and hot water tank inside our homes and this process is called HEATING. We are transferring the heat obtained to the water in our systems, therefore the name AIR-TO-WATER heat pumps.
Frequently asked questions
1. Air passes the heat exchanger outside called EVAPORATOR and the refrigerant gas absorbs heat from outside air and evaporates
2. The vapour passes into the compressor and by compression increases its
temperature and pressure
3. Hot vapour is condensed in the 2nd heat exchanger, the heat being passed via water onto Heating or Domestic Hot Water system
4. The liquid refrigerant passes back through the expansion valve, reducing its pressure ready to start the cycle again.
A heat pump’s efficiency is often referred to as a “Coefficient of Performance” (COP) and all heat pump manufacturers are giving this value for nominal conditions of 7 °C outdoor temperature and 35 °C flow temperature.
The Coefficient of Performance (or COP) describes the ratio of electrical power used to heating power produced under fixed input and output conditions by the heat pump unit only. A COP is used for examining the performance of a heat pump unit at ideal test conditions, usually in a laboratory.
COP of 4 means for every 1kW of electrical energy used, 4kW of useful energy is produced – a net 3kW of useful energy will be ‘free’ generated by the heat pump.
COP decreases with falling ambient air temperatures and rising flow temperatures
The Seasonal Performance Factor or Seasonal Coefficient of Performance (SPF or SCOP) describes the ratio of the amount of electrical energy used by all components associated with the heat pump system, to the amount of heat energy delivered to the heating system, over a long period of time (e.g. season or year).
SPF is a better indicator of performance for the purposes of examining the “real-life” performance of a heat pump than COP and takes in account the type of heating system installed.
Under the new EU regulation SEAI has implemented this in the New Heat Pump Methodology and by using their proposed Heat Pump Calculation Tool we can get accurate SPF’s based on data that every heat pump manufacturer has to provide.
SPF values may vary depending on the type of heat emitters used and aiming for a low flow temperature will result in high SPF figures. Ideally with an Air-to-water heat pump we should use an UFH – underfloor heating system because this only requires flow temperatures up to 35 °C, resulting in SPF’s over 5.
We can also use low temperature radiators, aluminium or steel panel or fan coils which require flow temperatures up to 55 °C, resulting in SPF’s around 400%. Comparing these two figures we can see that the UFH system compared with a Low temperature radiator / fan coil system is circa 20% more efficient.
The DHW production efficiency though for any heat pump it is not that high due to the high flow temperature required to heat the DHW cylinder. This figure is in around the 200% mark and takes in account that most air-to-water heat pumps require an electrical immersion to raise the temperature in tank to 60 °C, as an anti-legionella protection.
Both Monobloc (water connection) and Split (refrigerant connection) heat pumps have their advantages and where the Monobloc scores well for the ease of installation the Split has slightly higher efficiencies and can be used with integrated cylinder units, giving a more compact and small footprint solution, having all components built-in the indoor module.
At an early stage of the project the designer of the system has to take in account the type of heating system that will be installed working closely with the BER assessor. The reason is to make sure that the Air-to-water heat pump can comfortable meet the heating load of the house and provides enough renewables thermal contribution to meet Part L requirements; heat loss calculations should be done in accordance with current standards and regulations. In most new dwellings the DHW production is going to be done off-peak heating demand, therefore we can prioritize this during the night and mid-day when the heating demand is very low. As most air-to-water heat pumps are equipped with an electrical back-up heater, this can be conditioned to be used for heating, only if external temperatures fall below a specified point. This point is called equilibrium temperature and usually is set at -3 °C but in most cases this is not used for heating at all.
Manufacturers with tradition in the heat pump industry have their Air-to-water heat pumps designed specially to suit the European climate working even at outdoor temperatures of -25 °C. One key thing to remember is that the “heart and blood” of any heat pump, whether it’s Monobloc or Split, it’s the “compressor and refrigerant”. Therefore make sure before buying into any systems that the manufacturer of the heat pump has also got experience, knowledge and tradition in this field and the product complies with the Energy Labelling & Ecodesign directives.
Heat pumps can heat or cool down an indoor space and heat up a DHW cylinder by the means of a refrigerant gas that can evaporate even at -25 °C. The refrigerant inside the piping helps in transporting this energy between the inside and outside of your home. This is the reason why there is an indoor and outdoor unit. The substances used have such properties that the process is the most energy efficient and achievable with technology, which is safe to use. There are a few types of refrigerants that Daikin has invented and still owns the patent on them, such as : R410 and the most environmental friendly & energy efficient R32.