At IMS Heat Pumps, we strive to provide you with the most efficient and comfortable heating solutions tailored to your specific needs. When we install your air source heat pump, we will set the heat curve for you, ensuring optimal performance from the start. However, if you wish to make adjustments yourself, this guide will help you understand what a heat curve is, how to set it, and how it ensures your home remains comfortable while maximising energy efficiency.

What is a Heat Curve?

A heat curve, also known as weather compensation, defines the relationship between the outdoor air temperature and the flow temperature of the water in your heating system. Essentially, the flow temperature automatically adjusts according to the outdoor air temperature: it increases when it’s colder outside and decreases when it’s warmer.

Setting a Heat Curve

To set a heat curve for your air source heat pump, we follow these steps:

  1. Determine the Design Parameters:
    – Outdoor Design Temperature (DOT): This is the coldest temperature your area typically experiences. In the UK, this can range from -1°C to -5°C.
    – Indoor Design Temperature: The desired indoor temperature, usually around 21°C.
  2. Heat Loss Calculation:
    – We conduct a heat loss calculation for your property to determine how much heat is lost at a given temperature. This calculation uses the lowest average temperature for your region as a baseline.
  3. Designing the Heating System:
    – Using the heat loss calculation and the DOT, we design your heating system to maintain the desired comfort level. The lower the design flow temp the more efficient the system will operate at.
  4. Initial Settings:
    – Slope: Start with a slope based on initial design recommendations, for example, 1.0 for radiators and 0.8 for UFH.
    – Offset: Set the offset initially to 0.
  5. Adjust the Heat Curve:
    – Example: At an outdoor temperature of 0°C, the flow temperature might be set to 35°C to maintain an indoor temperature of 21°C. If the outdoor temperature drops to -2°C, the flow temperature might need to rise to 37°C.
  6. Fine-Tuning:
    – Monitor indoor temperatures over a range of outdoor conditions.
    – Make small adjustments to the curve until the indoor temperature remains consistent and comfortable.

Example:

Let’s assume the following conditions for a typical UK winter:

  • Outdoor Design Temperature: -2°C
  • Indoor Design Temperature: 21°C
  1. Initial Settings:
    – Slope: 1.0
    – Offset: 0
  2. Observation:
    – On a cold day (-2°C), the initial settings might indicate a supply temperature of around 37°C.
  3. Fine-Tuning:
    – If the indoor temperature is not reaching 21°C, increase the slope to 1.2.
    – If the indoor temperature is exceeding 21°C, reduce the slope to 0.8
  4. Further Adjustments:
    – Adjust the curve as needed to correct overall temperature trends.

Monitoring and Adjusting

If for any reason the building is not performing to the design, whether better or worse, the heat curve may need to be adjusted to maintain internal comfort levels.

Tools and Controls

Modern air source heat pumps in the UK come with intelligent controls that allow you to set and adjust the heat curve. These controls may also offer additional features such as:

  • Advanced Weather Control: Predicts the weather based on real-time weather data and automatically adjusts the heat curve.
  • Remote Monitoring: Allows adjustments via smartphone apps.

Below are the heat curves illustrating the setup and adjustments for an air source heat pump in the UK climate:

Conclusion

Setting a heat curve correctly for your air source heat pump in the UK ensures that the system operates efficiently and maintains a comfortable indoor environment regardless of outdoor weather conditions. The milder UK climate requires a less aggressive slope. This process may require some trial and error, but the result is a well-tuned heating system that provides consistent comfort and energy savings.

Video

We have created a short video tutorial on how to set the heat curve on your Vaillant air source heat pump, watch it below.

If you need any more information or assistance with your heat pump system, please feel free to contact us.