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What Is Weather and Load Compensation and Why Does It matter?
Weather and load compensation are the only ways you should be controlling your heating system in 2024. Especially in the race we are in to reduce our carbon footprint in the UK…
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Taking A Deep Dive Into Weather and Load Compensation
Weather and load compensation are the only ways you should be controlling your heating system in 2024. Especially in the race we are in to reduce our carbon footprint in the UK. Every little helps, right? These controls should be installed on any new gas boiler and heat pump installation as a bare minimum. If your Installer hasn’t specified this to you and can’t explain why, then please read on so you can make an informed decision as to what you are having fitted. I’ll begin by breaking down the guidance on what weather and load compensation are, before detailing why they are important.
What exactly is weather and load compensation?
Weather compensation is a control strategy that uses the current outside temperature as a reference, when communicating how much energy to put back into the house with the boiler. In doing so, it matches the current heating requirements with the heat loss. It does this by reducing the flow temperature that it is putting out, which has massive benefits in both gas boilers and heat pumps (more below). Imagine that it was 9 degrees outside the house and you were trying to reach a comfort level inside of 21 degrees. A weather compensated controller would communicate with the heat source to reduce the output to match.
Here’s some maths to help. Let’s say that your house needs 11kw of energy to heat it to 21 degrees when it’s -2 outside. There is a difference here of 23 degrees. This means that your house requires 0.48kw of energy for every degree of heat. If the outside temperature is 9 degrees then you will only require enough energy to raise the temperature by 12 degrees to reach 21 , which is about half of the energy needed when it’s -2. Therefore 12 times 0.48 = 5.76kw, or roughly half of the 11kw maximum needed at designed outside temperature.
A weather compensated controller will tell your heat source how many kw of energy to supply to the house as the temperature varies, keeping your house at a nice balanced temperature. This equals more comfort.
Load compensation does the same thing, but from the inside of the house. So instead of using the outside temperature as its point of reference, it would use the temperature of where the thermostat is located. Some of the smarter load compensation controls will learn how long it takes for your home to reach its desired temperature and calibrate themselves. Load compensation isn’t as advanced or efficient as weather compensation, but it is still a lot more efficient than a typical on/off controller, and is the bare minimum we install on all of our installations at Revolution Heating.
What happens when we don’t use any compensating controls?
Imagine you are driving a sports car down a straight road with lots of traffic lights. Instead of driving steadily towards the set of lights ahead of you, you speed up to them as fast as you can and break harshly when you reach them. In doing so, you miss where you were supposed to stop. Then when the lights go green you race off to the next set, breaking harshly once again when reaching them. Guess what – you miss them again! This is what happens when you use a typical on/off type controller that does not modulate the heat source. Your boiler or heat pump will fire at its maximum temperature that it is set to until it reaches your desired room temperature, before shutting off. Your radiators, however, will still be really hot and radiate extra heat into the property, overshooting the desired room temperature. You will then need to wait until the temperature drops below the desired room temperature to trigger a call for heat.
This cycle will repeat over and over. Not very comfortable either. Now imagine that you drive more carefully and see the traffic light changing in the distance, at which point you would slow down gradually and come to a rest. This is what a weather and load compensation controller will do – a mechanism that is more efficient, comfortable, and causes less wear and tear on your heating system (and racing car!).
Unfortunately we live in a world where installers are still fitting on/off type controls regularly. These were introduced to pre-condensing boilers when we had to have boilers running at high temperatures to reduce the condensation, as it would rot through the older boilers. The on/off controls would be used to control the high flow temperatures that are being delivered into the house. With modern boilers and heat pumps being more efficient at lower temperatures, it makes sense to move with the times and only install up to date controls that can reduce these flow temperatures when they can.
How does weather compensation work with a well designed heating system?
If we start from scratch and design a system completely from the bottom up – and do it properly – we can design the size of the radiators to reach the desired room temperatures that we require, without any thermostatic radiator valves. We can balance these throughout the house so they are designed to all reach their desired temperatures equally. In doing this we can even lose the internal room thermostat and just rely on the outside weather to dictate how much to heat the house by. This does normally require a little bit of setting up of the weather curve and is something that your installer should show you how to do upon commissioning!
Will any compensating controller work with my heat source?
The short answer to this is ‘No’. Different manufacturers use different languages to communicate with their controls and heat sources. This means that it takes a careful bit of planning to make sure that the correct controller is able to modulate your heat source. Generally speaking, if you use the controls from the manufacturer of the heat source that you have installed then this will normally work best. Especially when talking about heat pumps.
Compensating controllers and how they make condensing boilers more efficient
Modern condensing boilers will only ‘condense’ when the return temperature to the boiler is below 54 degrees. This means that anything above that is not actually getting any benefit from reusing the heat within the flue gases – the whole idea of a condensing boiler. A gas boiler is designed to have a differential temperature of 20 degrees between the flow and return. So if you set your flow temperature to 75 degrees, then your return should be 55 degrees and would be completely out of this condensing zone. By bringing the flow temperature as close to 54 degrees as possible, whilst still giving enough heat to your house, you will gain a whole lot of extra efficiency from your boiler as this will mean most of the combustion process is within the condense zone. There are other benefits to this, as discussed in our benefits of low temperature heating blog.
Compensating controllers and how they make heat pumps more efficient
A heat pump has a compressor in its refrigeration circuit that needs to be turned on so it can assist in extracting heat from the outside air. This compressor takes a big amount of electricity to get started, so reducing cycling times is key. A modulating control source will lower the temperatures for longer, helping to keep the compressor on. With on/off controls this will cycle the compressor, often causing poor efficiency and high running costs.
Why do compensating controls matter?
We are in a fight to save the planet we live on for future generations. Heating our homes contributes to around 18% of our greenhouse gas emissions in the UK, so we need to do all we can to reduce this as we aim to reduce our greenhouse emissions to net zero by 2050. We need to be looking at everything we can do to assist this vision. The installation of heat pumps will be a huge help for reaching this target. However, understanding that not every house has the budget nor space for a heat pump means that we still need to do everything we can with the gas boilers that we install. And whilst a gas boiler with weather compensation is less efficient than a heat pump, it is far more helpful than an inefficient gas boiler with on/off controls. As I said, every little helps!
Conclusion
So as you can see, by using weather and load compensation controllers we can reduce the flow temperatures more often when the higher temperatures are not required, meaning lots of extra efficiency by just using the correct controls. In my opinion you should just fit weather compensation wherever you can. It will save on energy for gas boilers and help even more in heat pumps to bring those efficiency levels up. It’s an easy and effective way for all of us to lower our carbon output. It may cost a little bit more to fit when upgrading some boiler types, but the positives in the long run will by far outweigh any cost upfront.
