ᐅ Airflow specification of the mechanical ventilation system for heating load calculation
Created on: 14 Oct 2022 01:44
J
JaiBee07
Hello everyone,
I think I need your expertise again.
Originally, I didn’t plan to install any ventilation during the house renovation, but after seeing how much heat loss the energy consultant calculated for the ventilation, I decided to install two decentralized ventilation units in the open kitchen-living area. I didn’t consult an expert for this.
Now, for the precise heating load calculation of the heat pump, the air volume flow rate of the ventilation is being requested, and before I give completely wrong information, I wanted to ask for your opinion on my calculation:
We’re talking about an approximately 57m² (614 ft²) open kitchen-living-dining space based on the floor plan. Ceiling height is 2.68m (8.8 ft). That results in a volume of about 153m³ (5,404 ft³). However, this space will have quite a bit of furniture such as a fitted kitchen, fireplace, large refrigerator, couch, sideboards, etc., which I’m subtracting from the room volume.
Let’s roughly subtract 10m³ (353 ft³), leaving 143m³ (5,048 ft³) of room air volume.
Now I come to the point where I’m unsure. I have two Blauberg Vento Expert A-50 units operating alternately—one blows air in while the other exhausts air out.
This should mean double the air moved, so everything times 2.
The fan has three speed levels with heat recovery:
Level 1: 8 m³/h (5 cfm)
Level 2: 15 m³/h (9 cfm)
Level 3: 25 m³/h (15 cfm)
Additionally, the datasheet states a maximum exhaust air volume flow of 50 m³/h (30 cfm).
Now I’m not sure which value to use. For noise reasons, most people seem to run the units at Level 2. Since I have two fans, that would be 2 x 15 m³/h = 30 m³/h (18 cfm). So that would be my volume flow rate in this room, right?
Or should I use the highest possible value of 2 x 25 m³/h, or a combination like two-thirds at Level 2 and one-third at Level 3?
I only need the room volume for the air exchange rate calculation (which with 30 m³/h would be 143 m³ / 30 m³/h = 0.21 air changes per hour, which is below the recommended 0.5).
Is there anyone here who knows better than I do?
I think I need your expertise again.
Originally, I didn’t plan to install any ventilation during the house renovation, but after seeing how much heat loss the energy consultant calculated for the ventilation, I decided to install two decentralized ventilation units in the open kitchen-living area. I didn’t consult an expert for this.
Now, for the precise heating load calculation of the heat pump, the air volume flow rate of the ventilation is being requested, and before I give completely wrong information, I wanted to ask for your opinion on my calculation:
We’re talking about an approximately 57m² (614 ft²) open kitchen-living-dining space based on the floor plan. Ceiling height is 2.68m (8.8 ft). That results in a volume of about 153m³ (5,404 ft³). However, this space will have quite a bit of furniture such as a fitted kitchen, fireplace, large refrigerator, couch, sideboards, etc., which I’m subtracting from the room volume.
Let’s roughly subtract 10m³ (353 ft³), leaving 143m³ (5,048 ft³) of room air volume.
Now I come to the point where I’m unsure. I have two Blauberg Vento Expert A-50 units operating alternately—one blows air in while the other exhausts air out.
This should mean double the air moved, so everything times 2.
The fan has three speed levels with heat recovery:
Level 1: 8 m³/h (5 cfm)
Level 2: 15 m³/h (9 cfm)
Level 3: 25 m³/h (15 cfm)
Additionally, the datasheet states a maximum exhaust air volume flow of 50 m³/h (30 cfm).
Now I’m not sure which value to use. For noise reasons, most people seem to run the units at Level 2. Since I have two fans, that would be 2 x 15 m³/h = 30 m³/h (18 cfm). So that would be my volume flow rate in this room, right?
Or should I use the highest possible value of 2 x 25 m³/h, or a combination like two-thirds at Level 2 and one-third at Level 3?
I only need the room volume for the air exchange rate calculation (which with 30 m³/h would be 143 m³ / 30 m³/h = 0.21 air changes per hour, which is below the recommended 0.5).
Is there anyone here who knows better than I do?
Well, decentralized kilowatt-hours in Push-Pull operation like this (at least that's how I understand it as a layperson) > a heat-retaining building element is heated on one side by outgoing air, while on the other side the incoming air is warmed again by this preheated element.
But overall, it’s far from the efficiency of a cross-flow heat exchanger in a central controlled residential ventilation system. The whole thing is often integrated in one device (in and out also alternating quickly). My brother-in-law (HVAC planner!) installed this in a rental apartment – incredibly noisy (calculations look good though ;-) ).
But overall, it’s far from the efficiency of a cross-flow heat exchanger in a central controlled residential ventilation system. The whole thing is often integrated in one device (in and out also alternating quickly). My brother-in-law (HVAC planner!) installed this in a rental apartment – incredibly noisy (calculations look good though ;-) ).
Sorry, I need to follow up because I'm still not completely clear on the values, and I need to provide the "heating load calculator" with something final and as accurate as possible.
According to the manufacturer's data sheet, the fan has the following capacities:
Airflow in ventilation mode (m3/h): Stage 1 = 15; Stage 2 = 30; Stage 3 = 50
Airflow in regeneration mode (m3/h): Stage 1 = 8; Stage 2 = 15; Stage 3 = 25
It seems that in regeneration mode, only half the airflow is assumed because the fan reverses direction and runs 50% of the time in the opposite direction. It appears that only the exhaust air or only the supply air is being considered.
However, I have two fans, and when looking at the supply air, for example, the second fan operates on supply air during the time the first fan operates on exhaust air. So, wouldn’t the supply airflow actually be double what’s listed under regeneration mode?
Based on this information, shouldn’t a volume flow of 30 m3/h be specified for Stage 2 then?
According to the manufacturer's data sheet, the fan has the following capacities:
Airflow in ventilation mode (m3/h): Stage 1 = 15; Stage 2 = 30; Stage 3 = 50
Airflow in regeneration mode (m3/h): Stage 1 = 8; Stage 2 = 15; Stage 3 = 25
It seems that in regeneration mode, only half the airflow is assumed because the fan reverses direction and runs 50% of the time in the opposite direction. It appears that only the exhaust air or only the supply air is being considered.
However, I have two fans, and when looking at the supply air, for example, the second fan operates on supply air during the time the first fan operates on exhaust air. So, wouldn’t the supply airflow actually be double what’s listed under regeneration mode?
Based on this information, shouldn’t a volume flow of 30 m3/h be specified for Stage 2 then?
i_b_n_a_n schrieb:
Well, the decentralized kWh in push-pull operation works like this (as I understood it as a layperson) > A heat-retaining building block is warmed on one side by outgoing air, while the incoming air is reheated on the other side by this pre-warmed block.Yes, exactly like that. In reversing units, it happens sequentially. First, the warm indoor air being drawn in preheats the ceramic. Then, when cold outdoor air is drawn in, it is preheated by the stored energy in the ceramic. Since the stored heat only lasts for a limited time, this process needs to be repeated continuously.
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WilderSueden14 Oct 2022 11:49JaiBee07 schrieb:
So, according to this information, you would already need to specify an airflow rate of 30m3/h at stage 2, right?Yes, in this case, you would reach 30m3/h since there are two fans operating in regeneration mode. And they should be wired so that both are not doing the same thing simultaneously.WilderSueden schrieb:
Yes, in that case you get 30 m³/h (18 cfm) because two fans are operating in regeneration mode. And they are wired so that they don’t both do the same thing.Yes, the system does this automatically when configured accordingly. One acts as the master, and the other adjusts its rotation direction opposite to the master.
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