Understanding COP (Coefficient of performance) is a key part of assessing your heat pump's performance. It's a measure of efficiency that assess how much heat your heat pump produces versus how much electricity it consumes. Generally speaking, we want to maximise COP as much as possible to help keep your bills low. But as this article will show you, it isn't everything.
COP, the weather and hot water
COP is heavily influenced by the weather. Colder outdoor temperatures mean the heat pump has to work harder, hurting efficiency and decreasing COP. The hotter the temperature you're targeting for your heating or hot water also has an impact.
Heating the hot water tank to 55c is less efficient than heating it to 45c - the typical rule of thumb is a 2.5-3% loss in efficiency for each 1c decrease in out side temperature or 1c increase in target temperature.
COP vs SCOP
COP: An instantaneous measure of efficiency - it describes how efficient your heat pump is at a given moment in time
SCOP: Also know as seasonal coefficient of performance, this metric measures your performance across the year. It accounts for seasonal differences in efficiency.
This is also the reason why heating cycles are more efficient than hot water cycles. When you heat the home with a heat pump, you typically average much lower flow temperatures - as low as possible - than when you heat hot water.
You might expect COP to be lower during Summer when it's warmer outside, but you'd be mistaken. In summer, your heating is generally off due to the warmer outside temperatures. This means that the only thing contributing to the COP figure is the hot water, which runs at a much lower efficiency than the heating.
However, your home is using much less electricity over all, which means that you're still saving money. This one reasons why many people like to use SCOP, which average out changes over the year.
Bad data
When your heat pump isn't doing much, the stats can start going a bit funky. The sensors heat generation can be inaccurate when measuring small amounts. However, so long as the total amount of electricity your heat pump uses remains low this isn't really anything to worry about.