How do I calculate the heating capacity for my pool heat pump?

The pool heat pump is a type of heating that needs to be given time.

In fact, such a mass of water to be heated represents a large amount of energy. To determine it (at least as an approximation), simply multiply :

• m: mass of water in kg
• Cp: heat capacity of water, always 4185 J.kg-1.K-1 (J = Joules, kg = kilograms, K = Kelvin)
• ΔT The temperature difference between the base water (municipal water used to fill the pool: 10°C) and the desired final temperature (30°C, for example).

This formula is written: Q = m.Cp.ΔT

Some examples of power calculation heat pump pool

Rectangular swimming pool 10 x 5m: calculating the power required to heat the water

Pool dimensions:

• Length l : 10m
• Width L : 5m
• Low depth Hb : 1m
• High depth Hh : 3m
• Average depth h : 1.5m

Calculation of the pool volume:

V= L x W x H = 10 x 5 x 1.5 = 75 m3

Now 1m3 = 1000dm3 = 1000L

1000L of water = 1000kg (to the nearest approximation)

So our pool contains 75,000kg of water.

Calculation of the quantity of heat Q to bring to heat at 30°C :

Q = m.Cp.ΔT (in Joules)

Q = 75,000 x 4185 x (30 - 10)

Q = 6'277'500'000 Joules

Calculation of the number of kilowatt-hours:

We know that 1 kWh = 3'600'000 J

1 kWh is the energy supplied by a 1 kW machine for 1 hour.

We simply divide Q by 3'600'000 and we get 6'277'500'000 / 3'600'000 = 1744 kWh

This is the amount of energy required to heat the pool to 30°C.

Calculation of the time required to deliver this quantity of energy Q

All we need to do now is find out how quickly we can deliver this energy to determine our pool heating time.

If we opt for a 12 kW machine, for example, it will take our pool heat pump 1744 kWh to deliver this energy. This quantity is 1744 / 12 = 145 hours.

With a pool heat pump capable of delivering a constant 12 kW, it will take around 6 days to heat the water body to 30°C.

With a pool heat pump capable of supplying 8kW constantly, it will take about 9 days (72 hours) to heat the pool to 30°C

It's better to go for a heat pump that can heat up in 4-5 days. This would require 15 to 18kW...

Circular swimming pool of 10m diameter : Power of the swimming pool heat pump

The logic is the same. Only the calculation of the pool volume changes.

Pool dimensions:

• Diameter : 10m
• Radius : 5m
• Depth : 1.5m

Calculation of the pool volume:

V = Pi x 5 x 5 = 118 m3

Calculate the amount of heat Q required to heat the pool water to 30°C :

Q = m.Cp.ΔT (in Joules)

Q = 118'000 x 4185 x 20 = 9'876'600'000 Joules

Calculation of the number of kilowatt-hours:

Number of kWh = 9'876'600'000 / 3'600'000 = 2743kWh

Calculate the time required to deliver this quantity of energy Q :

To heat the pool to 30°C in 120 hours (5 days) you need a power of 22-23kW.

We can see that the required powers are quickly consequent.

In our examples we have taken 30°C, a very comfortable temperature. But 28°C is more reasonable.

It is also necessary to take into account the natural elements. The wind or the rain which can increase the calculated times, and the sun which can decrease the duration.

Our power calculator for PAC Piscine

Calculate the power required for your pool heating system. This will give you an initial estimate of the power required, but it's a rough estimate in the sense that it doesn't take into account any pool enclosure, regional weather conditions, altitude, etc.

Sites that offer power calculators for PAC Piscine

On the following sites you will find a heating capacity calculator for your pool that will save you from going through the above calculation process.