As air source heat pump installers, we will set the weather compensation curve for you. It ensures optimal performance from the start.
However, if you wish to make adjustments yourself, this guide will help you understand:
- What a weather compensation curve (/heat curve) is
- How to set it
- How it ensures your home remains comfortable whilst maximising energy efficiency.
What is a weather compensation curve?
A weather compensation curve (also known as heat curve) is a setting for controlling the range in temperature of water in air source heat pumps.
It defines the relationship between the outdoor air temperature and the flow temperature of the water your heating system’s water.
Essentially, the flow temperature automatically adjusts according to the outdoor air temperature. So, it increases when it’s colder outside and decreases when it’s warmer.
Not having the right weather compensation curve is a fairly common heat pump problem. It applies to heat pumps of all sizes.
Setting a weather compensation
To set a weather compensation for your air source heat pump, we follow these steps:
1. Determine the design parameters
This is done based on two metrics:
- 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. (Remember, good heat pumps work fine in winter!)
- Indoor design temperature: The desired indoor temperature (usually around 21°).
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.
Other factors, like having underfloor heating working with your air source heat pump, might also make a difference to the settings.
4. Initial Settings
These are:
- 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
For 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. And make small adjustments to the curve until the indoor temperature remains consistent and comfortable.
Example weather compensation curve calculation
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.
And 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, the weather compensation 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 weather compensation 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.
Optimising these gives you the most comfortable temperatures and running costs.
Below are the weather compensation curves illustrating the setup and adjustments for an air source heat pump in the UK climate:
Conclusion
Setting a weather compensation (/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. But the process of setting the slop may still require some trial and error.
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 weather compensation 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.