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?
Even 55W still seems quite high to me, 105 is a disaster. One of the most important measurements should be the CO2 concentration. Have you ever measured that? Our system runs between 3 and 5V at different times; in the morning just before getting up, a burst of ventilation runs at 7.5V.
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stefanc8418 Dec 2018 22:56Well, actually it wasn’t really expected, or at least I didn’t expect it. The attic space is basically inside the building envelope. The roof (above the attic) has 24cm (9.5 inches) of insulation. Down to the living area, there are only 6 or 8cm (2.5 or 3 inches) installed. You might think that more heat is rising from below than escaping outward, right? The reason for this is not clear to me; it could also be due to some defect. But that’s the way it is now.
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stefanc8418 Dec 2018 23:07Lumpi_LE schrieb:
I still think 55W is quite a lot, 105W is a disaster..
One of the most important measurements should be the CO2 concentration. Have you measured that? Have you measured your own consumption? As I said, the actuator doesn’t measure very accurately. I still think the value is realistic. Take a look at the data Helios provides. At my current 5.5V (5.5V) it’s estimated to be about 35 to 40 watts, at 7.5V (7.5V) around 65 watts. Both with zero pressure loss (0 Pa). Realistically, the pressure loss is closer to 100 Pa (100 Pa), and consumption increases with every Pascal. I have fairly long duct runs. Unfortunately, the system hasn’t been properly balanced yet; hopefully a few watts can still be saved. But it could also be the opposite.
I don’t have a CO2 or VOC sensor, no. I mostly rely on my nose.
You can find fairly good and affordable devices to measure this (under 100€). I used one to log the CO2 concentration in every room over 2-3 days while I was adjusting the system.
I have the mechanical ventilation system (also Helios) connected to a separate electricity meter, which is also logged. During the day, it consumes about 750-800 watt-hours, so roughly 30 watts on average.
Pressure losses are quite high in my case as well (I believe around 180 Pa), because there is a 50m (164 feet) long earth-to-air heat exchanger installed before the mechanical ventilation system.
I have the mechanical ventilation system (also Helios) connected to a separate electricity meter, which is also logged. During the day, it consumes about 750-800 watt-hours, so roughly 30 watts on average.
Pressure losses are quite high in my case as well (I believe around 180 Pa), because there is a 50m (164 feet) long earth-to-air heat exchanger installed before the mechanical ventilation system.
Hello,
in principle, the unit of a central ventilation system is ideally sized for about 50% capacity. For example, if the calculated nominal airflow is 180 m³/h (106 cfm), you still need to account for the system’s static pressure. Typically, the system will then operate at around 200 m³/h (118 cfm). Therefore, the unit should deliver between 350 - 400 m³/h (206 - 235 cfm). This ensures the unit runs quietly and efficiently, while also leaving plenty of capacity for the boost ventilation setting.
in principle, the unit of a central ventilation system is ideally sized for about 50% capacity. For example, if the calculated nominal airflow is 180 m³/h (106 cfm), you still need to account for the system’s static pressure. Typically, the system will then operate at around 200 m³/h (118 cfm). Therefore, the unit should deliver between 350 - 400 m³/h (206 - 235 cfm). This ensures the unit runs quietly and efficiently, while also leaving plenty of capacity for the boost ventilation setting.
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UpperEast31 May 2019 12:56How is the volume flow rate calculated?
It should depend only on the number of occupants (+ dog, cat, opossum, ...) and not on the area.
It should depend only on the number of occupants (+ dog, cat, opossum, ...) and not on the area.
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