How to Properly Size a Pool Heat Pump

Heating or warming up a swimming pool with a pool heat pump is different from heating or warming it up with a traditional pool heater. What are traditional pool heaters? These are your electric pool heaters and heaters that use natural gas. The main difference for these types of heaters is that with your traditional pool heaters, they’re actually actively producing heat to warm up your pool, which is why their output is measured by BTUs (British Thermal Units). Pool heat pumps on the other hand simply transfer the heat from the air to your water, so computations and numbers like BTUs can be a little bit “off” as it is directly affected by the temperature of the air. The colder the air surrounding your heat pump, the less heat is being transferred to the water and vice versa.

In pool heat pumps, two values that we have to take note of are the COP and the kW output. These two numbers, coupled with the air temperature can give you a good picture of how much power and time is needed to heat up your pool.

COP stands for Coefficient of Performance, which basically just means how much heating is transferred to your pool for every unit used. For traditional heaters, this number is around 0.75 which means that for every 100 units of energy used by the heating unit, only 75 gets transferred to the pool water and the 25 is lost. While 75% energy transfer sounds “ok”, it pales in comparison when compared with energy efficient pool heat pumps from Madimack. How so? Well, depending on the model, the average COP of the residential pool heat pumps can be anywhere from 8 to 10! This means that for every 100 units of energy that are consumed by the unit, 800 to 1000 units are transferred to the pool! Talk about efficiency right?

Without getting too much into the scientific computations, the easiest way to do this is to assume (well, it’s not really an assumption, this is a number supplied by the manufacturer) that it takes 1.16 Wh to heat one litre of water up by one degree. Taking this number, we know that it takes 11.6kWh to heat up a 10,000 litre pool by one degree Celsius in an hour.

To further simplify things, we have created a table that can give you an idea of how fast (or slow) different sized pool heat pumps can raise the temperature of your water so that you can have a rough idea of the size you’ll need for your pool before going to look at the specific models.

Now you may think to yourself, wow, that looks like a lot of power, and yes it does look like it until we apply the COP factor. Let’s take for example the Water Technix Paradise heat pump with an average COP of 14, so if we have a model that’s outputting 18KW, we’re actually only using 1.8KWh because of the COP factor of 14! (Output divided by the COP Factor)

While it may sound like a good idea to get something small to save on the upfront costs, it is worth noting that unless you have a pool cover, your pool can lose up to 2C overnight! So it is always good to pick a pump that will take a maximum of 4 hours to raise the temperature by 1C so that we can maintain overnight water temperature and we can consistently maintain perfect swimming temperature throughout the swimming season.

Note: What to get for your pool? Find the volume of your pool, and pick a heat pump model with heating increase of 0.25 and above. The higher the number, the faster your pool heats up. For example, if you have an 50,000L pool then the minimum recommended size would be the 18KW model (0.27c per hour). If the exact size / wattage isn't available, pick the next size UP.

SEE ALSO: Extending the Swimming Season with a Pool Heat Pump

This is where pool heat pumps throw in the towel versus traditional pool heaters. Pool heat pumps will take a while to heat up the pool to the desired temperature so some planning will be required on your part. So aside from making sure that your pool heat pump will be able to overtake the heat loss during the night, the overall size of your unit will be vital in how fast your pool heat pump will heat up your pool to comfortable levels.

Don’t get scared of getting oversized pool heat pumps, once your water gets to the required temperature, it only takes a little bit of energy to maintain your temperature (see table) so depending on the pool size and heat pump size, it will only take a few hours of operation to maintain your pool water’s temperature at a comfortable level. And this boils down again to the COP factor. Larger models tend to have higher COP factors so this means that when it comes to maintaining water temperature, they actually use LESS energy than a smaller unit.

So there you have it, everything you’ll need to properly size your pool for an energy-efficient heat pump!