ᐅ Modulating Heat Pumps / Temperature Differential / Excessive Start Cycles

A modulating heat pump can adjust its kW output to match the demand.

With my modulating heat pump, you can set the differential, that is, the difference between the supply temperature and the return temperature.

Is this the parameter that controls the power output? In other words, does the kW output adjust so that a certain value of the differential is maintained?

What changes if I adjust the setpoint from 5°C (41°F) to 2.5°C (36.5°F) or to 8°C (46°F)?

If I have the problem that the heating turns off too quickly and causes too many startups—although all individual room thermostats are open and the heating curve has been minimized—can adjusting the setting for DHeizen (differential) positively influence this situation?

The main issue is likely that the system was oversized, with a modulation range of 3-12 kW for a heating demand of 6.3 kW.

Other points should also be checked or tested:
- Check and, if necessary, clean the dirt traps in the heating circuit/brine circuit
- Verify temperature sensors (supply/return)
- Inspect the bypass valve (possibly too far open?)
- Optimize hydraulic balancing (noticeably less heat reaches the upper floor compared to the ground floor when all individual room controllers are open)
- Limit the heat pump output to 3-6 kW or 3-9 kW

jx7 schrieb:

A modulating heat pump can adjust its kW output according to demand.

Does the flow rate also adjust automatically? A small temperature difference can lead to a high flow rate (because the heat pump simply cannot dissipate the heat – or it short cycles). A large temperature difference results in a low flow rate.

My understanding at the moment is:

When I increase the target temperature difference, the kilowatt output is reduced so that the flow rate through the underfloor heating is slower, allowing the heating water to cool down more and resulting in a larger temperature difference.

This would be beneficial in my case because the problem is that the heating system produces too many kilowatts of heat for the house to absorb quickly. This way, I can force the heating system to operate at lower kilowatt levels.

Is that correct?

nordanney schrieb:

Does the flow rate also adjust automatically? A small temperature difference can lead to a high flow rate (because the heat pump simply can’t get rid of the heat – or it cycles). A large temperature difference leads to a low flow rate.

Unfortunately, I don’t know. My guess was that the flow rate is regulated to achieve the desired temperature difference. But that is just a guess.

Is the flow rate proportional to the kW output, or does it operate independently?

jx7 schrieb:

Is the flow rate proportional to the kW rating, or does it operate independently?

I actually can't tell you that. I simply don't know. It probably varies from pump to pump – mine controls the interaction entirely automatically.