Very special residential ventilation needed for old buildings

Hello,

I have an old building and will replace old windows (almost 50% are 68 years old), possibly also replace the extremely poor insulation. In my eyes, this means I make my house more airtight. Inside the house, there was sometimes a draft with strong wind even with closed windows and slightly open doors. Since this air exchange will then be eliminated, I am thinking about a controlled residential ventilation with heat recovery. Ventilation in all rooms is out of the question because that would be an extreme installation effort. The house is already fully renovated inside. Central HRV probably also doesn't work for the same reasons. Now I am trying to find out if I could manage with a few decentralized systems. Some features would be important here because I would like to operate different rooms with one system (cost/space/effort).

Kitchen/Bathroom 1: Both are next to each other and would be important for the HRV. Here I would like to have a system with a humidity sensor that operates both. The catch is that it would have to switch to, or I would have to be able to switch to, the room that is currently humid. If I simply connect both rooms in parallel via piping, on the one hand the air exchange in the damp room would be only half and the distribution of supply and exhaust air in both rooms would not be exactly 50:50 and not exactly equal. So, in one room more air is exhausted and in the other more air is blown in. Overpressure arises and the air of one room is pushed into the house. If that is the currently humid room, then I push the moisture and possibly odors into the house.

Living room/Bedroom or Living room/Basement: Here a cold room is combined with a very warm room. I would need a 2-room HRV with separate heat exchangers. Or one that can heat the air to different extents. So already a larger device. Especially for the basement, we also want a ventilation system because we want to make it sporadically habitable, use it in winter for drying clothes, etc... But it is not well insulated and accordingly cold. The situation is similar with the bedroom, just less extreme. We could combine two rooms here. But I do not want, for example, to cool the living room with air from the cold bedroom and not heat the bedroom.

Smart HRV with heat recovery: Temperature is an issue for us. In winter, it is about warmth and heating costs. Unfortunately, our installer severely undersized the heating. I demanded larger radiators, but that is still not quite enough. In summer it gets very warm. Are there HRVs to which you can tell whether you want it cool or warm and which then work accordingly? Obviously, heat recovery always helps. What I mean is that when it is hot in summer, less heat exchange takes place during the day and when the device notices that it is cooler outside, it pumps very actively and tries to cool the room.

Decentralized HRV with heat recovery and small air conditioning: That is then the next level. Are there such combinations?

I hope you can help me a bit and I don’t get answers like “google” or “search function”… ;-) Of course, I have already searched but not found exactly these things. Except for the air conditioning, I have not searched there yet. Just occurred to me now.

Many thanks in advance,
Best regards
derMartin

New windows certainly make the house more airtight. But why do you now think you cannot do without various ventilation systems? Have you already had bad experiences with damp spots/mold?

What have you just renovated?

I would first insulate all easily accessible / inexpensive spots as much as possible: top attic ceiling/slopes, basement ceiling. This already raises the wall temperature in the critical corners.

What is undersized: the heating system (which is already an art to get right in a single-family house today) or the radiators?
Additional radiators can be easily retrofitted if needed, once the pipe routes are known.

What kind of exterior wall construction do you have?

In most cases, a mechanical ventilation system is not necessary; with proper ventilation behavior, the house should actually remain mold/damp spot free.
1-3 hygrometers also help here. That way, you always keep an eye on the indoor humidity and can counteract accordingly.

Installing a residential ventilation system in old basements can make sense, but it must then be controlled by both indoor AND outdoor temperature and humidity, otherwise you just bring in damp-warm air again. Alternatively and more cheaply: run a dehumidifier in the basement in summer if needed.

A ventilation system in all rooms is off the table, as this would require extreme installation effort. The house is already completely renovated inside.

It makes sense to renovate from the outside in, and window replacement also creates dirt.

Hello dertill,

But why do you now believe you can't do without various ventilation systems? Have you already had bad experiences with damp spots/mold?

I had a few slight mold spots. Nothing serious. But until now, the house has been anything but warm and tight.

What exactly have you renovated recently?

Floors, walls, furniture, heating, bathrooms, kitchen. Why? What does that have to do with the question?

I would first insulate all easily accessible / inexpensive areas as far as possible: top attic ceiling/slopes, basement ceiling. This will already raise the wall temperature in the critical corners.

Will do.

What is undersized: the heating system (which is already an art to get right today in a single-family house) or the radiators? Additional radiators can be easily retrofitted if necessary, once you know where the pipes run.

The radiators are too small. Yes, they can be retrofitted. On the one hand, I had bad experiences with heating installation and on the other hand, this is not the way I want to go. I waste too much energy. It might get a bit better with bigger radiators, but I want to reduce energy loss. Currently, I have a HWB of 180.

What kind of exterior wall construction do you have?

I can't say yet.

In most cases, a mechanical ventilation system is not necessary; rather, with reasonable ventilation behavior, the place should actually remain free of mold/damp spots. Hygrometers (1-3) also help here. With them, you always have the indoor humidity in view and can react accordingly.

Unless I'm not there. That happens quite often. Especially in winter, often up to a month. Also, for warmth and baby reasons, my wife is hard to convince to ventilate.

Installing a residential ventilation system in old basements can make sense, but it must then be controlled by both indoor AND outdoor temperature and humidity; otherwise, you just bring moist-warm air back in. Alternatively and cheaper: run a dehumidifier in the basement in summer when needed.

Yes, a dehumidifier is an option. I even have one. With 0.5 kW, however, it’s not very energy efficient.

It makes sense to renovate from outside to inside, and window replacement also makes a mess.

Depends. For example, if you want to move in, it’s good to have, say, a bathroom. Sure, you’re right. But there are practical reasons that sometimes prevent it.

Best regards
derMartin

Hello,

I have now answered these questions. Can someone answer my questions regarding (decentralized) controlled residential ventilation with heat recovery?

- Are there ones with separate "heat circuits"? That is, a system that ventilates a cold (basement) room and a warm one without pumping the heat from the living area into the basement? The alternative is obviously to have two systems.

- Is there the possibility to switch the air outlet? That you connect two rooms and, depending on the need, switch the air to one room. An exhaust air system with switchable outlet, preferably controlled by a humidity sensor, would be best. But that might be too extreme.

- How well can these systems work "intelligently"? That is, for example in summer, when you want it to be cool, ventilate little and as soon as the outside temperature is below the inside temperature, ventilate like crazy to cool the living area.

- Are these devices available in combination with an air conditioner?

Thanks in advance,
derMartin

- Are there any with separate "heat circuits"? That a system ventilates a cold (basement) room and a warm one without pumping heat from the living area into the basement? The alternative is obviously to have two systems.

Two systems, everything else is nonsense.

- Is there the possibility to switch the air outlet? That you connect two rooms and depending on demand switch the air to one room. With switchable exhaust air preferably controlled by a humidity sensor would be best. But maybe that’s too extreme.

Two systems, everything else is nonsense.

- How well can these systems work "intelligently"? That is, for example, in summer, when you want it cool, ventilate little and as soon as the outside temperature is below the inside temperature, ventilate like crazy to cool the living area.

Actually, not at all. The usual decentralized systems are there for ventilation and lack intelligence. Additional intelligence is not free either, but since decentralized systems are generally supposed to be as inexpensive as possible, well, you can guess the rest.

- Are these devices available in combination with an air conditioning system?

Well, you can combine anything with anything. Only then again intelligence is missing.

For this reason, there are central systems that leave no wishes unfulfilled (with appropriate equipment), where VRV, air conditioning, humidification, etc. are possible.

Floors, walls, furniture, heating, bathrooms, kitchen. Why? What does that have to do with the question?

It is sustainably easier and cheaper to achieve energy savings and mold prevention constructively without the use of additional technology and only if that (reasonably) doesn't work, to resort to permanently running technical systems. A residential ventilation system should not be the first choice for problem solving but only an addition or extra comfort.

. I waste too much energy. It might get a bit better with bigger radiators, but I want to reduce energy loss.

With a ventilation system you only reduce energy loss caused by active ventilation through opened windows. Especially in old buildings, this share compared to total losses is very small. If you really want to save heating energy, you should not start with the ventilation system.

I can't say yet.

If you want to reduce the energy loss in your house, you should find out the structure. What does your facade look like (clinker brick, plaster, wood)?, wall thickness? solid construction? building age? subsequent installations/modifications? - This information is sufficient for evaluation for now.

Unless I am not there. That also happens more often. Especially in winter and often for up to a month

If no one is in the house in winter and the building is permanently heated and you have no water damage inside, nothing will mold there, whether with or without a ventilation system, since no one in the house is adding moisture to the indoor air with their body or activities (showering, cooking).

Mold needs four things to grow: nutrients (wallpaper, dust, organic dirt), surface humidity of 70% or more, surface temperatures below 17°C, and a pH value below 9.

The colder the surface/air, the higher the relative humidity at the same absolute water content.
Warm air can hold absolutely more water than cold air.
If the air, for example, has 50% humidity at 22°C, it contains about 8 g of water per kg of air.
If this air cools down to 15°C in room corners, it still contains 8 g of water but has a relative humidity of about 75%. If it cools further, the 8 g water per kg of air eventually means 100% or more, and water condenses out of the air => fog.

Even if you have a ventilation system and your humidity stays at a constant 45-50%, you can still get mold in room corners if these are too cold and the relative humidity there then reaches 70% or more.

The goal should therefore be to increase the surface temperature of the most critical spots such as room corners or penetrations in the exterior wall.
This can be most easily achieved by insulating the roof slopes and the top floor ceiling (i.e., between the attic and the upper floor) and by insulating the underside of the basement ceiling. Affordable, easy to do yourself, and effective. This saves a lot of heating energy and reduces mold formation in room corners. Because of the insulation above/below the corners, the temperature there increases, the relative humidity decreases, and mold is deprived of its basis for growth.

Replacing windows is also a good point but don't forget the reveal areas. When replacing, re-plastering is usually necessary anyway; then you can also attach calcium silicate insulation boards there or at least apply lime plaster and silicate paint (pH value >10) in these areas.

Thanks to better windows and insulation of the top floor ceiling/basement ceiling, you will then need less energy for room heating and no larger radiators anymore. Insulating the roof slopes and the top floor ceiling also leads to less heat input from outside in summer! This makes it less hot in the house in summer.

If you have done all this and still have problems with mold in several places, you should consider a ventilation system.

EDIT: I overlooked that you want to make the basement habitable. Then basement ceiling insulation is useless because the basement is not cold.
BUT:
Heating a non-insulated basement from 1960 to make it habitable without insulating it is not possible or will have bitter consequences. Regardless of with or without a ventilation system. The surface temperatures of floor and wall are around 10°C all year round. Sealing the certainly existing outside air openings and heating it plus additional moisture input from laundry and people would lead to condensation water in the walls and floor. For habitation, external insulation of the basement walls is necessary, and even then the floor remains, which should only be insulated very carefully with expertise.