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2025

How to calculate the heat pump heating capacity?

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To calculate the heating capacity of a heat pump, you need to consider several factors related to the heat pump's performance. The heating capacity is typically expressed in kilowatts (kW) or BTUs per hour (BTU/h). The basic formula is:

1. Q = m × Cp × ΔT

Where:

Q = Heating capacity (kW or BTU/h)
m = Mass flow rate of the fluid (kg/s or lb/h)
Cp = Specific heat capacity of the fluid (kJ/kg·°C or BTU/lb·°F)
ΔT = Temperature difference between the supply and return fluids (°C or °F)

2. Step-by-Step Process:

Determine the Flow Rate of the Fluid (m):
- The flow rate can be found using the system specifications or can be calculated if the system’s volume and the desired temperature rise are known. For example, if you're using water as the heat transfer medium, you can calculate the flow rate based on the system’s demand.
- For water, the density is approximately 1 kg/L, so mass flow rate is roughly equivalent to the volumetric flow rate in liters per second (L/s).
Specific Heat Capacity (Cp):
- This is the amount of energy required to raise the temperature of a unit mass of fluid by 1°C (or 1°F). For water, Cp is approximately 4.186 kJ/kg·°C.
Temperature Difference (ΔT):
- This is the difference between the temperature of the fluid leaving the heat pump and the fluid returning to the heat pump. The higher the temperature difference, the higher the heating capacity.

3. Example Calculation:

Let’s say we have the following data:

Flow rate of water: 2 L/s (or 2 kg/s, assuming water)
Specific heat capacity of water: 4.186 kJ/kg·°C
Temperature difference: 10°C (from supply to return)

The heating capacity would be:

Q=2kg/s×4.186kJ/kg°C×10°C $Q = 83.72 \, \text{kW}$ Q =83.72kW

So, the heating capacity of the heat pump is 83.72 kW.

4. Factors to Consider:

Coefficient of Performance (COP): The COP of the heat pump indicates how efficient the heat pump is at transferring heat. A higher COP means the system is more efficient, and the heating capacity can be optimized by selecting a heat pump with a high COP.
Outdoor Temperature: The temperature of the source (ground, air, or water) affects the heat pump’s efficiency. Lower outdoor temperatures usually result in lower capacity.
Heat Pump Type: Air-source, ground-source, or water-source heat pumps will have different efficiencies and capacities depending on the medium they use.

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