Hello!
I'll start.
Heated area 200m2 (2,153 sq ft)
KfW 55 standard
Mechanical ventilation with heat recovery
Current outdoor temperature 6°C (43°F)
Heating energy consumption including hot water 35 kWh
Electricity consumption 9 kWh
COP 3.88
I'll start.
Heated area 200m2 (2,153 sq ft)
KfW 55 standard
Mechanical ventilation with heat recovery
Current outdoor temperature 6°C (43°F)
Heating energy consumption including hot water 35 kWh
Electricity consumption 9 kWh
COP 3.88
I used a calculator to estimate this. The calculation is only approximate, but at 23°C (73°F) and 60% relative humidity, there is about 12.3 g/m³ (0.77 grains/ft³) of water vapor in the air.
At 20°C (68°F) with the same relative humidity, it’s 10.4 g/m³ (0.65 grains/ft³), and at 15°C (59°F) with the same relative humidity, it drops to 7.7 g/m³ (0.48 grains/ft³).
Looking at it the other way: if you want to reduce the absolute amount of water in the room by half while keeping the same 60% relative humidity at 23°C (73°F), you would need to cool the room down to 11°C (52°F). Then, without any air exchange, that water would naturally condense in liquid form inside the room. This is just for illustration, of course. It’s not an absolute scenario since there is some air exchange happening when the window is open and the door is closed, but it’s not fast enough.
Simply matching the indoor relative humidity to the outdoor relative humidity is not enough when there are strong temperature differences. After ventilating, you need a much lower indoor relative humidity, especially if the indoor temperature does not drop significantly...
At 20°C (68°F) with the same relative humidity, it’s 10.4 g/m³ (0.65 grains/ft³), and at 15°C (59°F) with the same relative humidity, it drops to 7.7 g/m³ (0.48 grains/ft³).
Looking at it the other way: if you want to reduce the absolute amount of water in the room by half while keeping the same 60% relative humidity at 23°C (73°F), you would need to cool the room down to 11°C (52°F). Then, without any air exchange, that water would naturally condense in liquid form inside the room. This is just for illustration, of course. It’s not an absolute scenario since there is some air exchange happening when the window is open and the door is closed, but it’s not fast enough.
Simply matching the indoor relative humidity to the outdoor relative humidity is not enough when there are strong temperature differences. After ventilating, you need a much lower indoor relative humidity, especially if the indoor temperature does not drop significantly...
I’ve already mentioned cross-ventilation several times. It should also be clear that the cold air needs to be warmed up again to absorb more moisture. Heating – ventilation – heating – ventilation.
The results are clearly visible with @Alessandro; he just enjoys discussing.
The results are clearly visible with @Alessandro; he just enjoys discussing.
Neubauling28 Jan 2021 09:40I would recommend anyone who needs a clear illustration of humidity or the amount of water in the air to search for an h-x diagram. A picture (in this case: a diagram) really is worth a thousand words.
T
T_im_Norden28 Jan 2021 09:44The key factor for ventilation concerning moisture is the absolute water content in the air. This can mean that cold outside air contains more water than the warm indoor air, in which case ventilating would bring moisture into the house rather than remove it. To be sure, it is recommended to use a calculator that shows the water content at a given percentage of humidity and temperature.
A
Alessandro28 Jan 2021 11:32Cross-ventilation is only partially possible for me because I need to open the window in the hallway for it. Due to the open design, there is a draft on the ground floor, which is often not feasible with two small children.
Currently, I have the following values in the bathroom.
Standard relative humidity (RH) is about 55%
After showering (my wife and I both shower in the evening), RH is about 70-80%
After ventilating for 5-10 minutes, RH drops to about 35-40%
After that, with the door closed, RH rises again to about 55-60%.
Since moving in, the values have decreased by about 10% RH, so I don’t suspect a leak. My bathroom is tiled almost up to the ceiling everywhere, with a large shower where some water usually remains after showering. Three wet towels add to the humidity. Maybe this is normal, I’m not sure.
For comparison, I only have my parents’ 7 m² (75 sq ft) bathroom, also tiled up to the ceiling. When four people shower one after another there, no condensation forms on the mirror or the window.
I just hope it will improve over time and that some of the moisture comes from the residual humidity of the tile mortar.
@halmi: I enjoy discussing this, but I don’t see a difference whether I reach 35-40% RH through cross-ventilation or simple ventilation 😉
The humidity sensor is located quite centrally on the mirror at a height of 2.30 m (7 ft 7 in). I’ve also placed it in the shower once, where it usually shows 5% less than on the mirror. That’s why I would also rule out a leak or airtightness issue here.
Currently, I have the following values in the bathroom.
Standard relative humidity (RH) is about 55%
After showering (my wife and I both shower in the evening), RH is about 70-80%
After ventilating for 5-10 minutes, RH drops to about 35-40%
After that, with the door closed, RH rises again to about 55-60%.
Since moving in, the values have decreased by about 10% RH, so I don’t suspect a leak. My bathroom is tiled almost up to the ceiling everywhere, with a large shower where some water usually remains after showering. Three wet towels add to the humidity. Maybe this is normal, I’m not sure.
For comparison, I only have my parents’ 7 m² (75 sq ft) bathroom, also tiled up to the ceiling. When four people shower one after another there, no condensation forms on the mirror or the window.
I just hope it will improve over time and that some of the moisture comes from the residual humidity of the tile mortar.
@halmi: I enjoy discussing this, but I don’t see a difference whether I reach 35-40% RH through cross-ventilation or simple ventilation 😉
The humidity sensor is located quite centrally on the mirror at a height of 2.30 m (7 ft 7 in). I’ve also placed it in the shower once, where it usually shows 5% less than on the mirror. That’s why I would also rule out a leak or airtightness issue here.
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