ᐅ Mechanical ventilation with heat recovery – Is setting level 7 out of 9 a reasonable configuration?
Created on: 3 Jan 2018 21:30
S
stefanc84S
stefanc843 Jan 2018 21:30Hi 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?
Hello,
I am just starting to familiarize myself with the topic of mechanical ventilation with heat recovery, but maybe I can share a few thoughts based on my research so far.
My impression is that a larger system would be preferable, as it can run more slowly and therefore more quietly and energy-efficiently—you’ve already compared the data sheets, after all. Often, forum posts mention that owners of mechanical ventilation systems are unhappy because their units are too loud and sometimes even shut off in the evening or at night. This is frequently due to running the system at a high setting. I see this mainly as a comfort issue, but in the end, you will be living in this house for decades.
With a larger unit, you also have the option to increase the ventilation rate, for example, when you have guests, are cooking, or after heavy use of the bathroom. This flexibility is not available with a smaller system.
How costly would it be to purchase new ductwork and possibly enlarge any openings? Maybe you could even resell the old ducts?
If you say you planned the system together with the sales representative, maybe there is a possibility they could make an adjustment for you? The issue with pressure loss and the resulting system size might have also been noticeable to them...
Perhaps some other forum members with mechanical ventilation systems can confirm or refute these points. I am currently speaking only from theory.
Good luck!
I am just starting to familiarize myself with the topic of mechanical ventilation with heat recovery, but maybe I can share a few thoughts based on my research so far.
My impression is that a larger system would be preferable, as it can run more slowly and therefore more quietly and energy-efficiently—you’ve already compared the data sheets, after all. Often, forum posts mention that owners of mechanical ventilation systems are unhappy because their units are too loud and sometimes even shut off in the evening or at night. This is frequently due to running the system at a high setting. I see this mainly as a comfort issue, but in the end, you will be living in this house for decades.
With a larger unit, you also have the option to increase the ventilation rate, for example, when you have guests, are cooking, or after heavy use of the bathroom. This flexibility is not available with a smaller system.
How costly would it be to purchase new ductwork and possibly enlarge any openings? Maybe you could even resell the old ducts?
If you say you planned the system together with the sales representative, maybe there is a possibility they could make an adjustment for you? The issue with pressure loss and the resulting system size might have also been noticeable to them...
Perhaps some other forum members with mechanical ventilation systems can confirm or refute these points. I am currently speaking only from theory.
Good luck!
B
Bieber08154 Jan 2018 09:30stefanc84 schrieb:
But unfortunately, that is not enough, because pipes with a larger diameter would also need to be used between the distribution boxes and outside. From my own experience: When in doubt, I would always choose the larger nominal diameter!S
stefanc844 Jan 2018 12:12Thank you for the feedback. Of course, if in doubt, I would opt for the larger system – but the smaller one has already been purchased.
The loss from reselling it would likely be limited since I got the system at a very low price. The larger one costs about 800€ more, and I don’t expect to get such a good price again on a second purchase. Therefore, I estimate additional costs of around 1,200€. This assumes I can sell the parts I no longer need.
In the forum, some calculations are based on only 30m³ (1,060 cubic feet) per occupant, which leads to much lower values. Others consider an air exchange rate of 0.3 sufficient, whereas the Helios calculator usually ends up above 0.4.
The forum also recommends a utilization rate at rated ventilation between 50 and 67% – without addressing pressure losses.
Accordingly, the model 300 unit is still recommended for houses with around 200m² (2,150 square feet) of living space.
We have 145m² (1,560 square feet) of living space and, excluding the attic, an air volume of 395m³ (13,950 cubic feet). Including the attic, it’s 449m³ (15,860 cubic feet). The unit has a maximum airflow of 315m³/h (11,120 cubic feet per hour).
If I ignore pressure losses and calculate with the nominal capacity, as is usually done in the forum, this corresponds to a utilization rate of 50% without the attic and 57% with the attic.
The highest fan setting, INCLUDING pressure losses, is just sufficient for intensive ventilation at an air exchange rate of 0.6.
Therefore, I’m now a bit more relaxed and hope to achieve sufficiently good air quality after all.
Still, I would prefer the larger unit because it could run more quietly on a lower setting.
Ultimately, the suitability of the device apparently depends significantly on whether I ventilate the insulated but unoccupied attic or not. As a compromise, I’m thinking of setting only an air exchange rate of 0.15 there for moisture protection. No air will be used there, but without ventilation, almost no air exchange will occur, which I don’t think is good either.
Since there are no overflow openings into the living areas, I would set supply air on one side of the attic and exhaust air on the other side.
Does that sound reasonable? And what do you think about my 395/449m³ air volume and the system’s maximum of 315m³/h?
The loss from reselling it would likely be limited since I got the system at a very low price. The larger one costs about 800€ more, and I don’t expect to get such a good price again on a second purchase. Therefore, I estimate additional costs of around 1,200€. This assumes I can sell the parts I no longer need.
In the forum, some calculations are based on only 30m³ (1,060 cubic feet) per occupant, which leads to much lower values. Others consider an air exchange rate of 0.3 sufficient, whereas the Helios calculator usually ends up above 0.4.
The forum also recommends a utilization rate at rated ventilation between 50 and 67% – without addressing pressure losses.
Accordingly, the model 300 unit is still recommended for houses with around 200m² (2,150 square feet) of living space.
We have 145m² (1,560 square feet) of living space and, excluding the attic, an air volume of 395m³ (13,950 cubic feet). Including the attic, it’s 449m³ (15,860 cubic feet). The unit has a maximum airflow of 315m³/h (11,120 cubic feet per hour).
If I ignore pressure losses and calculate with the nominal capacity, as is usually done in the forum, this corresponds to a utilization rate of 50% without the attic and 57% with the attic.
The highest fan setting, INCLUDING pressure losses, is just sufficient for intensive ventilation at an air exchange rate of 0.6.
Therefore, I’m now a bit more relaxed and hope to achieve sufficiently good air quality after all.
Still, I would prefer the larger unit because it could run more quietly on a lower setting.
Ultimately, the suitability of the device apparently depends significantly on whether I ventilate the insulated but unoccupied attic or not. As a compromise, I’m thinking of setting only an air exchange rate of 0.15 there for moisture protection. No air will be used there, but without ventilation, almost no air exchange will occur, which I don’t think is good either.
Since there are no overflow openings into the living areas, I would set supply air on one side of the attic and exhaust air on the other side.
Does that sound reasonable? And what do you think about my 395/449m³ air volume and the system’s maximum of 315m³/h?
stefanc84 schrieb:
According to that, the 300-unit system is still recommended for houses with 200 sqm (2153 sq ft) of living space.I can definitely disagree with that. It is sufficient, yes, but not economical.
I have just under 150 sqm (1615 sq ft) and a 300-unit system, and experience has shown that this is okay. But add another 50 sqm (538 sq ft), and you’re back to your original situation.
For anything over 150 sqm (1615 sq ft), I would definitely choose a system that can circulate at least 400 cubic meters.
If you only ventilate the attic slightly, then your smaller system might be enough.
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