ᐅ Is a heat load calculation necessary when specifying desired indoor temperatures?
Created on: 6 Feb 2018 12:04
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PäddaHello.
I have often read in the forum that a heating load calculation is absolutely necessary. Recently, we attended a building trade fair and I spoke with three leading gas heating manufacturers. Each of them said that a heating load calculation with specific desired temperatures for individual rooms is unnecessary for a gas heating system because the capacity of the gas heater is always sufficient. According to the exhibitors, a heating load calculation is always performed anyway, but with standard room temperatures, for example, 18°C (64°F) for bedrooms and 21°C (70°F) for living rooms. This is regulated somewhere as a standard temperature. I then told them that we differ a bit from the standard and want 22°C (72°F) in the bedroom and 23°C (73°F) in the living room. The exhibitors said that this is completely irrelevant. With a gas heating system, these temperatures can always be achieved. The heating curve just needs to be adjusted accordingly.
They also said that the installation spacing of the underfloor heating pipes does not really matter. However, if a heat pump is possibly planned for installation at some point in the future, the pipe spacing should be reduced from, for example, 20cm (8 inches) to 10–15cm (4–6 inches).
What do you think about this?
I have often read in the forum that a heating load calculation is absolutely necessary. Recently, we attended a building trade fair and I spoke with three leading gas heating manufacturers. Each of them said that a heating load calculation with specific desired temperatures for individual rooms is unnecessary for a gas heating system because the capacity of the gas heater is always sufficient. According to the exhibitors, a heating load calculation is always performed anyway, but with standard room temperatures, for example, 18°C (64°F) for bedrooms and 21°C (70°F) for living rooms. This is regulated somewhere as a standard temperature. I then told them that we differ a bit from the standard and want 22°C (72°F) in the bedroom and 23°C (73°F) in the living room. The exhibitors said that this is completely irrelevant. With a gas heating system, these temperatures can always be achieved. The heating curve just needs to be adjusted accordingly.
They also said that the installation spacing of the underfloor heating pipes does not really matter. However, if a heat pump is possibly planned for installation at some point in the future, the pipe spacing should be reduced from, for example, 20cm (8 inches) to 10–15cm (4–6 inches).
What do you think about this?
Basically, the manufacturers are right. The gas heating system will always be sufficient.
However, a room-by-room heat load calculation is essential for designing the underfloor heating. Even a gas heating system is more efficient with a low flow temperature.
In addition, you have the option to switch to a heat pump.
Also (I believe I have heard) that high flow temperatures in underfloor heating can potentially cause health issues.
However, a room-by-room heat load calculation is essential for designing the underfloor heating. Even a gas heating system is more efficient with a low flow temperature.
In addition, you have the option to switch to a heat pump.
Also (I believe I have heard) that high flow temperatures in underfloor heating can potentially cause health issues.
The burners themselves already have more than enough capacity. In this respect, it is fair to agree that no calculations are necessary for sizing the burner.
The other aspect is economic operation. And in this regard, the industry, apparently including the manufacturers, seems stuck in the past and incapable of doing better. What a revelation.
The other aspect is economic operation. And in this regard, the industry, apparently including the manufacturers, seems stuck in the past and incapable of doing better. What a revelation.
Alex85 schrieb:
The burners themselves already have enough capacity. In this respect, one can agree that no calculation is necessary for sizing the burner.
Another aspect is economical operation. And here, the industry—apparently up to the manufacturer—is stuck in outdated thinking and simply cannot do better. What a self-revelation.Okay, I understand. The burners and the gas heating system themselves can handle it, but other construction measures are also important to implement. I assume you mean, among other things, the installation spacing?!
Heating installers often skip the heating load calculation, especially for natural gas boilers. They simply install a standard 20kW unit in a 150m² (1,615 sq ft) new build, assuming it will definitely be sufficient because "that's how it's always been done." Heating installers are then "to blame" when the temperature doesn’t reach exactly 22°C (72°F) in every room at -15°C (5°F) outside, especially if the bathtub is being filled at the same time. That’s why they usually oversize the system by 50-100%, figuring the additional 200€ (the cost of a larger unit) won’t matter.
It is then considered "normal wear and tear" that the boiler frequently cycles on and off, never runs at full capacity except for domestic hot water preparation, and that after 3-5 years the burner needs replacement and the heat exchanger gets clogged.
Gas condensing boilers do have a wide modulation range (usually 20-100%), but the system should be sized so that this range is fully utilized rather than constantly operating only at 20-40%. I recently had my heating replaced myself, and it took a lot of effort to convince the plumber that for my 140m² (1,507 sq ft) house with triple glazing, 30cm (12 inches) of floor ceiling insulation, and basement ceiling insulation, I do NOT need a 24kW boiler. And guess what? At -15°C (5°F) last week, the 16kW boiler kept every room comfortably warm with a supply temperature of 52°C (126°F) (without underfloor heating).
For individual rooms, at least a reasonable estimate of the heating load based on the exterior wall area and room size should be made. It is true that almost any room can be heated by adjusting the supply temperature in combination with a gas boiler, but this is not always possible with underfloor heating. The bottleneck is always the most critical room—the one with the largest ratio of exterior wall area to volume and hydraulically the furthest from the boiler. This room’s heating surface should be generously sized, as this is crucial for the required supply temperature.
It is then considered "normal wear and tear" that the boiler frequently cycles on and off, never runs at full capacity except for domestic hot water preparation, and that after 3-5 years the burner needs replacement and the heat exchanger gets clogged.
Gas condensing boilers do have a wide modulation range (usually 20-100%), but the system should be sized so that this range is fully utilized rather than constantly operating only at 20-40%. I recently had my heating replaced myself, and it took a lot of effort to convince the plumber that for my 140m² (1,507 sq ft) house with triple glazing, 30cm (12 inches) of floor ceiling insulation, and basement ceiling insulation, I do NOT need a 24kW boiler. And guess what? At -15°C (5°F) last week, the 16kW boiler kept every room comfortably warm with a supply temperature of 52°C (126°F) (without underfloor heating).
For individual rooms, at least a reasonable estimate of the heating load based on the exterior wall area and room size should be made. It is true that almost any room can be heated by adjusting the supply temperature in combination with a gas boiler, but this is not always possible with underfloor heating. The bottleneck is always the most critical room—the one with the largest ratio of exterior wall area to volume and hydraulically the furthest from the boiler. This room’s heating surface should be generously sized, as this is crucial for the required supply temperature.
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