ᐅ Mechanical ventilation with heat recovery – Is setting level 7 out of 9 a reasonable configuration?
Created on: 3 Jan 2018 21:30
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stefanc84
Hi everyone,
We installed our mechanical ventilation system ourselves, which was planned by a trading representative of H******.
They calculated the nominal ventilation rate at 147 m³/h (147 cubic meters per hour) and selected a device with a maximum capacity of 300 m³/h (300 cubic meters per hour). My own calculations resulted in a slightly higher nominal ventilation rate, partly because we have an insulated, unoccupied attic without windows that I think should be included (?). Also, they didn’t include stairwell areas and assumed a slightly lower ceiling height. This isn’t a big issue, as the difference is not substantial and the valves can still be adjusted during commissioning.
However, I came across the pressure loss calculation in the planning manual. No calculation like this was done previously, and even though it seems obvious now, I hadn’t thought about it before. I realize that a professional installation company would probably have done this calculation properly, rather than just a trading agent.
Anyway, I calculated a pressure loss of about 94 Pa (Pascal) for the longest duct run. According to this, the device would need to run continuously at level 7 out of 9. This obviously results in more noise and power consumption compared to using a more powerful device running only at level 5, according to the technical specifications.
We could possibly replace the unit with a larger one. But it’s not that simple, since larger diameter ducts would also need to be used between the distribution boxes and outside. These ducts are not yet installed, but have already been purchased.
How critical do you consider this situation? Is operating at level 7 out of 9 an acceptable design? After all, the example calculation in the planning manual uses the same device for similar data.
Do you have any comparable data from your systems that you could share with me?
We installed our mechanical ventilation system ourselves, which was planned by a trading representative of H******.
They calculated the nominal ventilation rate at 147 m³/h (147 cubic meters per hour) and selected a device with a maximum capacity of 300 m³/h (300 cubic meters per hour). My own calculations resulted in a slightly higher nominal ventilation rate, partly because we have an insulated, unoccupied attic without windows that I think should be included (?). Also, they didn’t include stairwell areas and assumed a slightly lower ceiling height. This isn’t a big issue, as the difference is not substantial and the valves can still be adjusted during commissioning.
However, I came across the pressure loss calculation in the planning manual. No calculation like this was done previously, and even though it seems obvious now, I hadn’t thought about it before. I realize that a professional installation company would probably have done this calculation properly, rather than just a trading agent.
Anyway, I calculated a pressure loss of about 94 Pa (Pascal) for the longest duct run. According to this, the device would need to run continuously at level 7 out of 9. This obviously results in more noise and power consumption compared to using a more powerful device running only at level 5, according to the technical specifications.
We could possibly replace the unit with a larger one. But it’s not that simple, since larger diameter ducts would also need to be used between the distribution boxes and outside. These ducts are not yet installed, but have already been purchased.
How critical do you consider this situation? Is operating at level 7 out of 9 an acceptable design? After all, the example calculation in the planning manual uses the same device for similar data.
Do you have any comparable data from your systems that you could share with me?
S
stefanc844 Jan 2018 12:38Ok, then we agree that the attic space will decide. The planning tool shows the same: with an attic, the 300 mm (12 inches) option is no longer available.
Damn... Now I have the choice between buying more material, noise, or less ventilation.
Damn... Now I have the choice between buying more material, noise, or less ventilation.
We did not ventilate the attic through the mechanical ventilation system with heat recovery. This doesn’t make much sense unless the attic is equally well insulated!
In our house, the mechanical ventilation system has 3 settings (which I can program both in terms of intensity and duration). According to the manufacturer’s calculation, the minimum ventilation is about 160 cubic meters per hour (cbm/h), the “normal ventilation” is 230 cbm/h, and the maximum ventilation is 310 cbm/h. The house is one and a half stories with roughly 165 square meters (1,775 square feet) of living space.
During the final inspection and instruction, all air inlets and outlets were measured to ensure they matched the planned values. Only the openings were adjusted accordingly, not the ventilation unit itself.
In my opinion, these systems only work properly if they have been correctly calculated, correctly installed, and accurately measured! (Air-to-water heat pump and mechanical ventilation system, etc.)
In our house, the mechanical ventilation system has 3 settings (which I can program both in terms of intensity and duration). According to the manufacturer’s calculation, the minimum ventilation is about 160 cubic meters per hour (cbm/h), the “normal ventilation” is 230 cbm/h, and the maximum ventilation is 310 cbm/h. The house is one and a half stories with roughly 165 square meters (1,775 square feet) of living space.
During the final inspection and instruction, all air inlets and outlets were measured to ensure they matched the planned values. Only the openings were adjusted accordingly, not the ventilation unit itself.
In my opinion, these systems only work properly if they have been correctly calculated, correctly installed, and accurately measured! (Air-to-water heat pump and mechanical ventilation system, etc.)
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stefanc844 Jan 2018 13:58Yes, the insulation is very high, and the airtight envelope is located on the outside. Of course, it needs to be properly balanced. But even if you fully open the valves, the pressure loss on the way to the valve does not disappear. The system must be designed for this. With proper planning, this is the case. In our situation, the calculations may have been somewhat optimistic, or the attic was not taken into account.
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Baumfachmann15 Jan 2018 16:53Hi, the most common mistake is choosing a system that is too small. Opt for the larger one.
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stefanc8418 Dec 2018 09:02Hi,
I wanted to share some practical experience since we have now been living in the house for 8 months.
In summer, I operated the device at the calculated nominal capacity (lower during heat). I believe it was 7.5V from a maximum of 10V. So, relatively close to the limit. The noise was noticeable in some rooms but not disturbing.
Now, in winter, despite the heat recovery, the air is quite dry, about 40%. I also activated the power measurement of my KNX switching actuator and was quite shocked by the reported consumption of 105 W. The actuators are not always very accurate, but a closer look at the technical data of the mechanical ventilation with heat recovery system shows that the stated power consumption values refer to very low air resistance. So my 105 W could well be realistic.
Another point is that despite the heat recovery, cool air is blown into the house around the clock.
I have now reduced it to 5.5V, which is slightly less than the calculated "reduced" ventilation. And what can I say? At least now in winter, it is more than sufficient. Power consumption dropped to 55 W, and the system is no longer audible.
I’m curious about next summer; hopefully, it will still be adequate then. So far, my concerns and yours have proven unfounded. Maybe it has to do with our building method.
Installing the device in the attic space turned out to be not so ideal. Although insulated, it is not only insulated against the outside but also towards the living space. Over time, it cools down quite a bit. Currently, it is 13°C (55°F). I believe this also "pre-cools" the supply air into the rooms.
I wanted to share some practical experience since we have now been living in the house for 8 months.
In summer, I operated the device at the calculated nominal capacity (lower during heat). I believe it was 7.5V from a maximum of 10V. So, relatively close to the limit. The noise was noticeable in some rooms but not disturbing.
Now, in winter, despite the heat recovery, the air is quite dry, about 40%. I also activated the power measurement of my KNX switching actuator and was quite shocked by the reported consumption of 105 W. The actuators are not always very accurate, but a closer look at the technical data of the mechanical ventilation with heat recovery system shows that the stated power consumption values refer to very low air resistance. So my 105 W could well be realistic.
Another point is that despite the heat recovery, cool air is blown into the house around the clock.
I have now reduced it to 5.5V, which is slightly less than the calculated "reduced" ventilation. And what can I say? At least now in winter, it is more than sufficient. Power consumption dropped to 55 W, and the system is no longer audible.
I’m curious about next summer; hopefully, it will still be adequate then. So far, my concerns and yours have proven unfounded. Maybe it has to do with our building method.
Installing the device in the attic space turned out to be not so ideal. Although insulated, it is not only insulated against the outside but also towards the living space. Over time, it cools down quite a bit. Currently, it is 13°C (55°F). I believe this also "pre-cools" the supply air into the rooms.
stefanc84 schrieb:
Installing the unit in the attic space turned out to be not as great as expected. Although the attic is insulated, it’s insulated not only on the outside but also towards the living area. In any case, the attic cools down quite a bit over time. Right now it’s 13°C (55°F). I think this also causes the supply air into the rooms to be somewhat “pre-cooled.”That was to be expected. Despite many opinions suggesting it works, a mechanical ventilation system with heat recovery inside the conditioned building envelope remains the best option.
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