Hybrid heat pump, boiler and thermostat
If you have a hybrid heat pump, you are probably very curious about how often the hybrid heat pump is turned on and how often the boiler is turned on. It is important to remember that you have a hybrid heat pump. This means that the hybrid heat pump will not always be used, but that sometimes the boiler has to step in. This is especially true at times when the heat demand is greater than what the hybrid heat pump can supply.
The thermostat (Anna or Adam HA) is connected to some hybrid heat pumps via OpenTherm. This is a digital protocol in which information can be sent and received. Some examples of hybrid heat pumps that support OpenTherm are:
- Techneco Elga
- Remeha Elga Ace
- Groupe Atlantic Aurea Hybrid Add-on
What does the thermostat do?
The Anna and Adam HA are smart thermostats that can calculate the ideal boiler temperature at the right time to heat your home. The only thing that a thermostat sends to the hybrid heat pump is the intended boiler temperature.
What does the hybrid heat pump do?
The hybrid heat pump receives this intended boiler temperature. The heat pump will then decide what to do with this: when will the water be actually heated, how much it will be heated and if the heat pump or boiler will heat. The hybrid heat pump therefore decides itself whether the heat pump or boiler is switched on.
The decision process of hybrid heat pumps to switch on the heat pump or boiler differs per brand and type. The required boiler temperature is always taken into account. If it is higher than what a heat pump can supply, only the boiler can supply that temperature. If the temperature is in the range of what the heat pump can supply, it can be chosen whether the intended boiler temperature is close to the current boiler temperature or far from it. Some of the different types of behavior we see in practice are:
- If the intended boiler temperature is close to the current boiler temperature, the heat pump first tries to switch on the heat pump and check whether the heat pump can make it. If the intended boiler temperature is far from the current supply temperature, the boiler switches on immediately.
- The heat pump always tries to switch on the heat pump first to try to reach the required boiler temperature.
- Instead of the heat pump or boiler, some types can also switch on the heat pump and boiler at the same time.
Optimizing the thermostat
The thermostat only sends the intended boiler temperature and does not decide whether the hybrid heat pump or the boiler is switched on. But as you read above, some hybrid heat pumps do look at how high the boiler temperature is and whether it is close to the current boiler temperature. In the Anna and Adam HA there are a few settings that ensure that a lower boiler temperature is required.
Heating Settings
Go to the heating settings:
- Open the Anna or Adam HA in the Plugwise Home app or login via connect.plugwise.net
- Click on the three bars of the menu at the top left.
- Go to Settings > Heating System > Heating > Advanced settings
Adjust the following:
- Set the heating profile to Eco. This heats as economically as possible and is particularly suitable for heat pumps.
- Only with Anna: Adjust the maximum preheating time to 300 minutes.
- Lower the maximum boiler temperature. Note: Not all hybrid heat pumps support this setting and is therefore not always adjustable.
- Click Save.
Heating schedule
If you set a heating schedule then Anna and Adam HA can start preheating. With this, the room will be at the right temperature according to the schedule. This allows Anna and Adam HA to start heating in advance. By preheating, lower boiler temperatures can be used and there is a greater chance that the hybrid heat pump can handle this lower temperature itself.
As soon as you adjust the temperature by hand, Anna and Adam HA see this as a direct heat demand that must be met as quickly as possible. A high or even the maximum set boiler temperature will therefore be required. This can often be higher than what the hybrid heat pump can deliver. There is a good chance that the hybrid heat pump will immediately switch on the boiler and only later switch to heating via the heat pump.
Analyzing the behavior of the hybrid heat pump
You can see the graphs of the supply and return temperatures at Anna and Adam HA. The graphs are only visible in the web interface when you are at home:
- Log in via connect.plugwise.net
- Click on the three bars of the menu at the top left
- Go to Measurements
- Click the Boiler tab at the bottom right
Even if you have a hybrid heat pump, seen from the Anna and Adam HA, the heat pump is seen as a boiler. That's why the word boiler is used everywhere. The hybrid heat pump gives the temperatures and modulation levels to the Anna and Adam HA. There is only 1 boiler temperature and 1 return temperature in your pipes, so the difference between what the heat pump does and what the boiler does is indistinguishable. If you know that a heat pump cannot deliver very hot water, and a boiler can, you can deduce when the hybrid heat pump has probably been on.
In the top graph you can see the following:
- The black line is the intended boiler temperature. So this is what Anna and Adam HA send to the hybrid heat pump.
- The red line is the boiler temperature. The blue line is the return temperature. This information comes from the hybrid heat pump and/or boiler.
- The green line is the pressure.
- Note: Not all hybrid heat pumps provide the boiler temperature, return temperature or pressure via OpenTherm. If this information is not there, it will not be displayed. The information can be from the hybrid heat pump or the boiler.
In the bottom graph you can see the following:
- The black line is the modulation level of the hybrid heat pump or boiler.
- The red line is the on or off status of the hybrid heat pump or boiler.
- Note: This information comes from the hybrid heat pump and/or boiler.
Below is a good example of an OpenTherm hybrid heat pump and boiler.
- In this example you see that a intended boiler temperature starts at 10:50 am at 40°C. The supply temperature starts at 20°C and gradually increases to 30°C. This is most likely the hybrid heat pump itself that is heating because these are very low temperatures. Also because the temperature rises slowly, it will probably be the hybrid heat pump since it just has limited power.
- After a while you see that the boiler temperature suddenly shoots up to 56°C. This can only be because the hybrid heat pump has decided to switch on the boiler. Only a boiler can deliver so much power so quickly. Please note, it cannot be deduced from this whether the hybrid heat pump itself also is turned on.
- At around 3:00 PM, the intended boiler temperature drops to 40°C. This is because the room has reached the set temperature and a lower temperature is needed to keep the room at that temperature. This temperature is a temperature that hybrid heat pumps are able to deliver. From this moment on you see another difference, the boiler temperature is a lot more stable and quiet, there are no large peaks and dips. This behavior is much closer to a heat pump than to a boiler. The boiler temperatures at a boiler are often more erratic.
- In the lower graph we see the modulation level. It is not visible whether this comes from the hybrid heat pump or the boiler. And this also differs per type of boiler and whether the boiler is connected to the hybrid heat pump via OpenTherm. In this example, we only see a modulation level in the first section. Together with the top graph, this can lead to the assumption that this probably came from the boiler. Since there was no modulation level after 15:00, this will probably mean that the boiler was not turned on later.
- You can see that the hybrid heat pump was probably not on all the time. This is also logical, the requested boiler temperature was higher than what the hybrid heat pump can deliver. The hybrid heat pump therefore decided to switch on the boiler at a certain point. You can see that the hybrid heat pump was probably switched on most of the day.
Do you have any questions?
We completely understand that you may still have questions because you want to heat the most efficiently and use the hybrid heat pump as much as possible. With the above explanation you better understand which part the thermostat does and which part the hybrid heat pump does. In short, who you can ask your question to:
- Do you have a question about the intended boiler temperature (the black line in the top graph)? Then you can ask Plugwise your question.
- Do you have a question about the boiler temperature, the return temperature, the pressure, the modulation level or the on/off status? Then you can ask your question to the manufacturer of your hybrid heat pump.