ᐅ Leaving the underfloor heating thermostat permanently on? A question for clarification
Created on: 1 Nov 2019 01:46
M
maduutoHello, we are about to build a house and will have a heat pump with underfloor heating. I often read online that the valves should always be left open so the heat pump doesn’t have to work against a closed heating system. Now I’m wondering, how does this work? I set the room thermostats to, for example, 21 degrees Celsius (70°F). As long as the room temperature is below 21°C (70°F), everything is fine. But if it goes above that, either because the heating has warmed the room beyond 21°C (70°F) or due to external heat sources, the valve closes.
So what exactly is meant by the advice to keep the valves always open? As I said, up to 21°C (70°F) they are open anyway. Maybe you can help clarify this?
Best regards and thanks
Pascal
So what exactly is meant by the advice to keep the valves always open? As I said, up to 21°C (70°F) they are open anyway. Maybe you can help clarify this?
Best regards and thanks
Pascal
The key terms are supply temperature and heating curve.
The heat pump heats the water in the heating system. The temperature of the water is called the supply temperature (from the heat pump to the underfloor heating).
This supply temperature is, for example, determined based on the outdoor air temperature. However, not entirely automatically—it can be set manually, for instance, 0°C (32°F) outside = 25°C (77°F) supply temperature.
If the heating curve is set incorrectly, the heat pump "produces" a higher supply temperature than necessary. The underfloor heating then warms the room more than needed, causing the room thermostat to close the heating circuit.
The goal is to adjust the heating curve so that the heat pump reaches exactly the supply temperature required for the desired indoor temperature.
This saves energy and is also gentler on the heat pump equipment.
Note, this is a simplified and condensed explanation. There are very detailed explanations available online.
The heat pump heats the water in the heating system. The temperature of the water is called the supply temperature (from the heat pump to the underfloor heating).
This supply temperature is, for example, determined based on the outdoor air temperature. However, not entirely automatically—it can be set manually, for instance, 0°C (32°F) outside = 25°C (77°F) supply temperature.
If the heating curve is set incorrectly, the heat pump "produces" a higher supply temperature than necessary. The underfloor heating then warms the room more than needed, causing the room thermostat to close the heating circuit.
The goal is to adjust the heating curve so that the heat pump reaches exactly the supply temperature required for the desired indoor temperature.
This saves energy and is also gentler on the heat pump equipment.
Note, this is a simplified and condensed explanation. There are very detailed explanations available online.
We bought a house with a heat pump, and now I have similar concerns because I believe the previous owners, who were elderly, didn’t have much understanding of the technology. Does anyone have a link or resource on how to proceed with optimizing the heating curve and related settings?
B
boxandroof1 Nov 2019 13:14Thermostats shorten the time during which the underfloor heating is actively heating by switching it on and off. Conceptually, a shortened heating time is similar to installing a smaller radiator instead of a large one.
To achieve 21°C (70°F) inside the house, a smaller radiator would need to operate at a higher flow temperature (for example, 35°C (95°F)) compared to a very large radiator (for example, 26°C (79°F)). At a representative outdoor temperature of +2°C (36°F) (air source), the temperature difference the (air) heat pump must overcome is:
a) with thermostat: 35°C - 2°C = 33 K
b) without thermostat: 26°C - 2°C = 24 K
A frequently overlooked characteristic of heat pumps is that the smaller the temperature difference, the more efficient the heat pump is at producing the same amount of heat. Therefore, as large as possible and continuously operated heating surfaces increase the efficiency and performance factor of the heat pump and reduce electricity consumption for the same heating result. For this reason, it makes sense, for example, to keep rooms like central hallways heated continuously.
In practice, using thermostats often goes hand in hand with an excessively high heating curve, a buffer tank that accepts arbitrarily high temperatures, and an oversized heat pump. Hydraulic balancing and heating surface design in the rooms are often neglected in this setup. The heating installer has minimal work during planning, and the homeowner is happy because the rooms heat up and the temperature can be adjusted as desired. The downside is unnecessarily high energy costs.
To achieve 21°C (70°F) inside the house, a smaller radiator would need to operate at a higher flow temperature (for example, 35°C (95°F)) compared to a very large radiator (for example, 26°C (79°F)). At a representative outdoor temperature of +2°C (36°F) (air source), the temperature difference the (air) heat pump must overcome is:
a) with thermostat: 35°C - 2°C = 33 K
b) without thermostat: 26°C - 2°C = 24 K
A frequently overlooked characteristic of heat pumps is that the smaller the temperature difference, the more efficient the heat pump is at producing the same amount of heat. Therefore, as large as possible and continuously operated heating surfaces increase the efficiency and performance factor of the heat pump and reduce electricity consumption for the same heating result. For this reason, it makes sense, for example, to keep rooms like central hallways heated continuously.
In practice, using thermostats often goes hand in hand with an excessively high heating curve, a buffer tank that accepts arbitrarily high temperatures, and an oversized heat pump. Hydraulic balancing and heating surface design in the rooms are often neglected in this setup. The heating installer has minimal work during planning, and the homeowner is happy because the rooms heat up and the temperature can be adjusted as desired. The downside is unnecessarily high energy costs.
Alright, but at some point, I still need to regulate the temperature, either due to external heat or if it actually gets warmer than 21°C (70°F), right?
Without a thermostat, wouldn’t it eventually get too warm on its own, even if only slowly? So, with a well-balanced underfloor heating system, is it safe to simply turn it off at 21°C (70°F), even if the temperature only approaches that level gradually? My idea would be to set the thermostat to 21.5°C (70.7°F) so that the underfloor heating can comfortably operate up to 21°C (70°F) as intended, and if it gets warmer due to external heat, the controller would just switch off at 21.5°C (70.7°F). Is this reasoning correct?
Without a thermostat, wouldn’t it eventually get too warm on its own, even if only slowly? So, with a well-balanced underfloor heating system, is it safe to simply turn it off at 21°C (70°F), even if the temperature only approaches that level gradually? My idea would be to set the thermostat to 21.5°C (70.7°F) so that the underfloor heating can comfortably operate up to 21°C (70°F) as intended, and if it gets warmer due to external heat, the controller would just switch off at 21.5°C (70.7°F). Is this reasoning correct?
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