Weather Compensation and Load Compensation for Adam
A common discussion point in the heating industry at the moment is weather compensation. But what is it, and how does it work? To answer this, let’s firstly discuss the “old fashioned” way of doing things…
The old fashioned way
The heating strategy in the domestic sector has typically always been for a heat source (boiler) to target a fixed flow temperature. Usually this would be set on the temperature dial on the boiler itself. This is the flow temperature that the boiler would continuously target and achieve. The boiler would regulate according to this using an internal thermostat (or temperature sensor), connected to the flow pipe itself.
In the bad old days, this target flow temperature would have typically been set to around 75°C! This means that the boiler would have always tried to achieve this temperature, no matter what the load condition was.
Now, the load of a property is not static. It changes with the outside ambient temperature. The colder it is outside, the higher the heating load and the warmer it is outside, the lower the load.
Usually, the size of radiators would be designed to accommodate the property’s peak load condition (the worst case, when it’s really cold outside). Without going into detail, it’s important to know that a radiator’s output power is dependent on its temperature, meaning the hotter it is (relative to the room), the more powerful it is.
Based on this, it would make sense that under lower load conditions (when it’s warmer outside) that the radiators would automatically reduce in temperature, so that their output matched the current heating load. However, this could only happen if the boiler was able to reduce its target flow temperature.
As we know from earlier, if the boiler is only able to target one temperature all of the time (which would be set to accommodate the peak load of the property), then under any other lower load condition, the radiators would be delivering too much power. This would cause the property to overheat.
The conventional way to combat overheating is with the use of room thermostats and thermostatic radiator valves (TRVs). These are often referred to as “on/off” controls. They either simply switch the boiler off or stop the flow of hot water from entering the radiators. Either way, this strategy always promotes boiler cycling, which is not a good thing!
This old fashioned way of temperature control is analogous to driving with your feet on the accelerator and brake pedal at the same time!
As mentioned above, it would make sense to change the radiator temperatures in response to a property’s heating load. And that’s exactly what weather compensation does!
Using an outdoor temperature sensor, these control systems can automatically change the target flow temperature on a constant basis. The colder it is outside, the higher the flow temperature and the warmer it is outside, the lower the flow temperature.
This massively reduces boiler cycling and increases system efficiency, as well as many other benefits.
Take a look at this article from Heat Geek on the benefits of low flow temperature heating systems:
The flow temperature that the boiler targets is adjusted according to something called a heat curve (compensation curve). A heat curve is basically the visual representation of the relationship between the outside temperature and the target flow temperature. These are configurable, so can be fine tuned to suit the design of a system.
In theory then, if the heat curve is perfectly configured, there would be no need whatsoever for internal thermostats or sensors to regulate room temperature. Weather compensation would simply make the radiators the correct temperature for any load condition, which would result in a constant and steady room temperature.
Unfortunately however, properties are subject to solar and internal gains. These are basically uncontrollable heat gains from either the sun and other things in the house that generate heat like computers, ovens and even people. Because of this, the theoretical ideal heat curve becomes less appropriate.
Weather compensation uses two points of measurement; the flow temperature and the outside temperature. Load compensation uses an additional, third point of measurement, the internal temperature. This gives the system the ability to automatically adjust and fine tune the pre-set heat curve and target flow temperature, in real time. This means that the boiler is constantly targeting the correct flow temperature to achieve the desired room temperature, no matter what is going on inside the property.
This ultimately results in stable internal temperatures, reduced boiler cycling, durability and importantly, higher efficiencies.
Check out this article from Heat Geek that goes into greater detail on weather and load compensation.
Written by Adam Chapman - Ecotechnician - Heat Geek