Glossary of terms
Leaving water temp
This is the temperature of the water the heat pump is circulating through your system. We set this as per your design to get you the greatest efficiency possible. The lower the leaving water temperature the more efficient the system.
Outside Ambient temperature
In weather, ambient temperature refers to the current air temperature —the overall temperature of the outdoor air that surrounds us. When indoors, ambient temperature is called room temperature. The standard average outside ambient temperature in the UK is 7°c and this is the temperature that most heat pumps systems are designed to work at optimum efficiency. However, we design your heat pump to work at optimum efficiency at -2°c. This means that you will have lower running costs compared to a system designed for optimum performance at 7°c.
A weather compensation control system can help the heat pump to work more efficiently and reduce electricity consumption. It monitors both the internal and external temperatures and adjusts the heat pump leaving water temperature accordingly. It can adjust the system leaving water temperature to match a heat output closer to the needs of the home, adjusting the system before the house starts feeling too cold or too hot.
Coefficient of Performance (COP)
COP (Coefficient of Performance) is a measure of efficiency. The efficiency of any machine or system can be calculated as the ratio of amount of work done by the machine to the amount of work given to the machine. In the case of a heat pump, its efficiency is the ratio of useful heat energy produced to electrical energy consumption. A COP of 2.5 means that the heat pump supplies 2.5 times as much heat energy to the system as it consumes in electrical energy.
The first law of thermodynamics tells us that energy can neither be created nor destroyed and this makes it hard to understand how a machine can generate more energy than it consumes. You’ll even find the odd Internet forum where someone states this and claims heat pump efficiency of more than one is “scientifically” impossible. The answer here is that COP measures how efficient a heat pump is at turning electrical energy into usable heat. It doesn’t do this by creating energy or being more than 100% efficient. It does it by using heat energy already present in the outside air. COP will be higher when outside air temperature is higher, as less electrical energy input will be needed to generate a given heat output.
Seasonal Performance Factor (SPF)
Where COP gives us efficiency of a heat pump at any given time, SPF gives us the same but for annual performance of the heat pump. Outside temperature is obviously lower in winter and higher in summer and this affects the amount of work the heat pump needs to do. At lower outside temperatures the heat pump will need more electrical energy to produce a given heat output, meaning that the system is less efficient.
As a result, the COP will be different through the seasons and SPF encompasses this by considering the annual performance of the system. The SPF of a heat pump is the ratio of annual heat generated to the annual electricity consumed for the operation of the heat pump.
As a formula this is calculated as:
SPF = Total heat output per annum / Total electricity consumed per annum
SPF tells how efficient a heat pump is on average.