Hot Tub Air Source Heat Pump

What is a hot tub air source heat pump?

Essentially, an air source heat pump is a reverse cycle refrigeration circuit. Refrigeration technology has been around for a very long time; in fact, the first commercial fridge was designed back in the 1800s.

How does a Hot Tub Air Source Heat pump Work?

Firstly, we need to understand the basics of Thermodynamics. Surrounding air contains thermal energy, and heat is naturally drawn to cold. Believe it or not, there is thermal energy even below 0 degrees centigrade. Absolute Zero is, in fact, -273.15 degrees centigrade. So, a hot tub air source heat pump captures this thermal energy from the air and transfers it to the hot tub water using electricity. However, the energy it captures is far greater than the electricity used. Because this energy it absorbs requires no fuel, it is extremely energy and environmentally efficient.

Basic Refrigeration Circuit

There are four main components of an Air Source Heat Pump:

  1. Compressor: pressurizes the refrigerant gas, essentially a pump with a reciprocating piston.
  2. Condenser: the refrigerant gas entering the condenser is hot and pressurized by the compressor. The condenser then cools the refrigerant by converting it into a liquid high-pressure state by allowing ambient air or water to flow over the condenser, and a heat transfer takes place.
  3. Expansion Valve: produces a pressure drop, and the hot liquid cools and goes into the evaporator.
  4. Evaporator: hot liquid turns back into a cold gas and picks up heat from the ambient air and enters the compressor as a warm refrigerant gas. It is then compressed under higher pressure again, becoming a hot gas before entering the condenser, and the cycle continues.

How efficient are Air Source heat pumps?

Hot tub air source heat pumps are more efficient than hot tub electric heaters because the amount of heat they produce is more than the amount of electricity they use. With regards to a hot tub electric heater, they are 100% efficient, which essentially means for every 1 kW of electricity in, they produce 1 kW of heat energy out. A hot tub air source heat pump can be over 700% efficient, depending on the ambient air conditions.

The efficiency and heat produced by an air source heat pump for every unit of electricity used is known as the Coefficient of Performance (CoP). This is an important point when considering a hot tub air source heat pump, as purchase cost will vary dramatically. Air source heat pumps and the heat output are based on this, and you will see they are sized according to the ambient air conditions, the COP will vary.

Air source heat pump CoP is calculated in this example: the heat pump has an electrical power input of 1 kW and a heat output of 8 kW. The remaining 7 kW are obtained from the environment. To calculate the CoP, you divide the heat output by the electrical input, which in this example results in a CoP of 8.

For more Info.

Engie Hot Tub Air Source Heat Pump

Power Saving Comparison

What are the expected purchase and installation costs?

Again, when considering purchasing a hot tub air source heat pump, prices can vary dramatically, and you will see all sorts of crazy deals and prices. Prices can vary from as little as £200.00 to £3500.00. So, you need to ask a few important questions:

Hot Tub Air source Heat pumps can either be on/off compressor type – Very cheap and not as efficient and will not last as long. Or inverter-driven, very efficient and more expensive.

Heat exchanger material – Decent heat pump heat exchangers are made from Titanium.

COP – What is the kW output rating at certain ambient conditions? – Decent air source heat pumps will operate from 15 degrees down to minus 15 degrees Celsius.

Size of heat pump at various ambient conditions – Essentially, for a hot tub water volume from 1000 litres to 1300 litres, you would require a heat pump around 8 kW and above. For swim spas, you would require a minimum of 12 kW.

The expected cost of a decent hot tub air source heat pump, once you have carried out all your research, you should expect to pay between £2000 – £2500.00 installed.

Expected payback when considering this purchase can vary between 18 months to 3 years depending on location, frequency of using your hot tub, and your energy tariff.

The lifespan of a decent air source heat pump is a good 10 to 15 years. Maintenance is minimal, apart from cleaning around the condenser and evaporator. The refrigeration gas will need to be recharged at some point. A hot tub air source heat pump will save up to 75% of hot tub electrical running costs.

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