ᐅ Extending a Ground Source Heat Pump System to Heat a Small Indoor Pool

Hello everyone,

Would it be feasible to connect an additional heating circuit for a small indoor pool (9 sqm (97 sq ft) surface area) to a geothermal heat pump (Ecoforest C3 3-12 kW HTR EH with 2x 99 m (325 ft) boreholes)?

The capacity of the heat pump should actually be sufficient, both considering the ground loop (2x 99 m (325 ft)) and the heat pump itself (12 kW):
- It is not an outdoor pool that cools down significantly at night.
- The initial heating of the pool could take place during the summer.
- The pool’s heat is not lost but remains inside the house.
- If the capacity is not enough during the coldest winter months to heat both the house and the pool simultaneously, it would not be a problem; the pool simply would not be heated during that time.
- In an emergency, the pool’s internal heater (4 kW electric heater) could also be used.

Here are all the relevant details:
Currently, 190 sqm (2045 sq ft) of underfloor heating and the domestic hot water for 5 people run through the geothermal heat pump.
The house has nearly KfW-55-standard:
Final energy demand: 21.4 kWh/(m²·a)
Primary energy demand: 51.4 kWh/(m²·a)
Thermal performance of the building envelope: 0.25 W/(m²·K)

Room dimensions:
5.08 m x 4.65 m x 2.31 m (16.7 ft x 15.3 ft x 7.6 ft)

Pool size:
246 cm (width) x 460 cm (length) – external (8.1 ft x 15.1 ft)
213 cm (width) x 427 cm (length) – internal (7.0 ft x 14.0 ft)
Desired water temperature: 28°C (82°F)

The basement is a waterproof concrete shell with excellent insulation. The house was built in 2016 and nearly meets KfW-55-standard.

I would appreciate knowledgeable answers and/or experiences from homeowners!

To raise the temperature of your nearly 13m³ (460 cubic feet) pool by just ONE degree, you need about 14.5 kWh of energy! (assuming a water depth of about 1.4m (4.6 feet))
What target temperature are you aiming for? How much temperature do you lose when the pool is not in use? (Does the pool have an insulating cover?)
Building a pool is expensive, but operating it is even more costly. ;-)

i_b_n_a_n schrieb:

To raise the temperature of your nearly 13m³ (460 cubic feet) by just ONE degree, you need about 14.5 kWh of energy! (I’m assuming about 1.4m (4.6 ft) water depth)
What target temperature do you have? How much temperature do you lose when not in use? (Does the pool have an insulating cover?)
Building a pool is expensive, operating it is even more costly ;-)

Thank you for the reply!

The pool is 1.22 m (4 ft) high, water depth somewhat less, let's estimate 10,000 liters (2,640 gallons).

The pool has an insulating cover when not in use.

The question is, how many degrees does the pool lose (28°C / 82°F water temperature)?

If it’s one degree, I calculate about 11.6 kWh per day for 10,000 liters, which corresponds to 0.5 kW * 24 hours.

A 12 kW heater should be able to handle that on about 90% of the days in the year, right?

I’m afraid I have to disappoint you; a well-insulated hot water tank loses about 1 degree per day. For your pool, I would expect even more.

The exact amount can only be estimated (by me). I would heat it to the desired 28°C (82°F) with the electric heater, then cover it and measure again after 24, 48, and 72 hours without reheating. That way, you’ll have realistic values.

i_b_n_a_n schrieb:

I have to disappoint you there; a well-insulated hot water tank loses about 1 degree per day. I would expect more for your pool.

However, the hot water tank is at 60°C (140°F), and the pool is at 28°C (82°F).

The pool is not installed yet, but I am currently planning the room preparation. The question is whether to install a heating circuit there that can then be connected as a pool heater via a heat exchanger.

i_b_n_a_n schrieb:

I’m afraid I have to disappoint you; a well-insulated hot water tank loses about 1 degree Celsius (1.8°F) per day.

However, the tank is considerably warmer (above 40°C / 104°F) and has a less favorable volume-to-surface ratio. That brings me to the question: what kind of pool is this supposed to be? As a plunge pool after the sauna, it’s too warm; as a wellness pool, it’s too cold; and it’s too small for swimming.