PROBLEMS AND SOLUTIONS

MOLD

Mold, a type of fungus, thrives in moist environments and can quickly colonize various surfaces, including walls and ceilings. It can trigger allergic reactions and cause health issues. To tackle mold effectively, it's crucial to implement preventive measures that target its root causes:

CONTROL MOISTURE LEVELS
Mold requires moisture to grow, so keeping indoor humidity levels below 60% can significantly inhibit its development. Consider using dehumidifiers in areas prone to dampness, such as basements and bathrooms, and promptly repair any leaks or water damage.

MONITOR CONDENSATION
Condensation on windows and cold surfaces can create ideal conditions for mold growth. To prevent this, insulate cold surfaces, such as pipes and windows, and use weather stripping to seal gaps and minimize air leakage.

IMPROVE VENTILATION
Proper ventilation is key to reducing moisture buildup indoors. Ensure that bathrooms, kitchens, and laundry rooms are adequately ventilated and open windows periodically to allow fresh air to circulate throughout the home. Make sure that no furniture, for example a cupboard, is placed directly next to the wall. To ensure proper ventilation there should be about three fingers of room between the furniture and the wall of your buidling (as this is something you can do now, so please stand up and do it).

RELATIVE AIR HUMIDITY

Ideally your ventilation should ensure the following parameters depending on the room usages.

room usage	living room	bedroom	kitchen	bathroom	office	children's room	basement
ideal temperature (in °C)	20	16-18	18	23	20	21	10-15
ideal temperature (in °F)	68	60.8-64.4	64.4	73.4	68	69.8	50-59
ideal relative air humidity (in %)	40-60	40-60	50-60	50-60	40-60	40-60	50-60

The ideal relative air humidity range is 40% to 60%. It shouldn't be neither to high (to prevent mold) nor to low (to maintain respiratory function, including the bronchial passages).

Ideally, you should air the room four times a day for five minutes in January, February and December, ten minutes in March and November, 15 minutes in April and September, 20 minutes in May and October and 30 minutes in June, July and August.

DOING THE MATH

FORMULAS
The relative air humidity shows us, how much water vapour is in the air relative to how much water vapour the air could potentially contain at a specific temperature. The corresponding formula is: relative air humidity = partial vapor pressure / saturation vapor pressure = absolute air humidity / vapor density

WINTER EXAMPLE
Let's assume an outside temperature of 5°C (41°F) and a relative air humidity of 60%. The inside temperature is 20°C (68°F) and we want to calculate change in the relative air humidity if the air comes inside and heats up.

The saturation vapor pressure at 20°C (68°F) is 0.023 bar and at 5°C (41°F) it is 0.009 bar. The partial vapor pressur is 0.6 * 0.009 = 0.0054 bar and the same inside and outside the building (otherwise you wouldn't be able to open the door ; ) ). The relative air humidity calculated by using the formula introduced before is: 0.0054 / 0.023 = 23% (< 60%).

If the air gets warmer, the relative air humidity decreases.

SUMMER EXAMPLE
So now we calculate with an outside temperature of 30°C (86°F) and a relative air humidity of 60%. The inside temperature is still 20°C (68°F) and we want to calculate change in the relative air humidity if the air comes inside and cools down.

The saturation vapor pressure at 20°C (68°F) continues to be 0.023 bar and at 30°C (86°F) it is 0.042 bar. The partial vapor pressur now is 0.6 * 0.042 = 0.0252 bar. The relative air is: 0.0252 / 0.023 = 109% (> 100% and > 60%).

If the air gets colder, the relative air humidity increases. Excess moisture in the air changes its aggregate state and condenses out, whereby these damp spots represent ideal conditions for the formation of mold.

VENTILATION SYSTEMS

As it is hard to maintain optimal values just by opening the windows regulary, in many cases it can be a good idea to install an automatic ventilation system which uses sensors and calculate optimal ventilation times regulary by itself. (They can also help with other issues, for example: reducing dust and pollens causing hay fever; ensuring better air quality and, compared with open windows, fewer mosquitoes come in and heat exchangers can save heating costs through heat recovery (however, this factor is usually overestimated economically, as we will see later))

We recommend using a decentralized solution, mainly for cost reasons. Centralized system, especially if you try to put them in place subsequently in homes already build, don't show a good return on investment in most cases.

There are many solutions out there, just search for something like - decentralized ventilation system - on the Internet.

COSTS
The costs vary from about 500€ to 800€ or 540$ to 860$ per unit (values from 04-26-2024; Germany) Let's assume taking a product for 500€ (540$). Depending on the size of your building you need two to three units, in most cases three, so that makes about 1500€ (1620$) for the devices. Now we have to add the installation costs of about 500€ (540$) for the electrician and 350€ (370$) for the core drilling so the total initial costs are approximately 2350€ (2530$) You can also do the installation yourself and rent a core drilling machine.

The operating costs are about 5€ (5.35$) electricity costs and, if available, usually around 20€ (21.40$) for the filters (normally two per device, which should be changed once a year, or maybe twice a year if you suffer from allergies). If you want to, you could also argue that the device in fact creates a surplus during its operation, because ventilation accounts for around 15% of a household's total heating requirement (for example, with a total of 4200 kWh, this would be 630 kWh) and the corresponding costs can be lowered thanks to the use of heat exchangers. However, this effect is rather small, the savings then amount to around 60€ (64$) per year, according to experience, depending on the efficiency level of the heat exchanger (whereby many of the figures there are also likely to be exaggerated ...), but this can hardly compensate for the purchase costs over the entire service life of the appliance. A ventilation system is therefore more a matter of comfort, so that you don't have to constantly open the window yourself and thus prevent mold formation.

HOW MOST VENTILATION SYSTEMS WORK
In most cases it works by using a pendulum mechanism: First, air is blown into the inside of the building for some time and then the propeller switches the direction of rotation and blows air out again. The heat is stored in a heat exchanger made of ceramic for example. It stores the heat from the one flow and gives it back to the other later on. Normally everything is placed inside one tube and this tube fits entirely into the wall so the devices are relatively small and easy to hide.

WHAT TO DO NOW
If you should consider a ventilation system to be useful for your case you now have to decide which one to choose, so please search again for something like - decentralized ventilation system - on the Internet.

The following table tries to compare the characterisctics of most other ventilation systems with those of the TVS.

characteristic	most ventilation systems	TVS
initial costs	about 1500€ (1620$) for three units (+ installation and core drilling)	depending on the used moduls, about 1500€ (1620$) for three units (see how we CALCULATE COSTS) (+ installation and core drilling)
heat exchanger efficiency	lower, because the pendulum mechanism works by storing the heat in relatively short moduls and the transmission curve is wavelike	higher, because of the counterflow mechanism ensuring constant maximum temperature differences resulting in higher transmission values and the possibility to expand the segments modulary (but not so important anyways, as we stated above, just overengineering xd)
airflow volume/speed	slightly below 50% because of the pendulum mechanism and the time needed to change flow directions with just one propeller (but it should be sufficient anyways, because the ventilation system is not working all the time so we still have options there)	100% because of the counterflow mechanism and the use of two propellers (also sufficient of couse, the surplus is just overeingineering again)
sound volume	louder, because the propeller is inside the wall	quieter, because the propellers are outside
filtering	lower, because the pendulum mechanism first sucks in but then blows everything back again after the direction of flow changes (and the constant alternation of warm and cold also leads to a constant alternation of dry and moist and thus facilitates the cultivation of bacteria inside the ventilation system)	higher, because of the counterflow mechanism ensuring constant maximum filtering, always blowing out dust and pollen and permanently filtering incomming air (and the filters are easier to exchange, because they aren't inside your wall but next to it)
design	usually unremarkable, small, easy to hide	ugly, much bigger, following the approach to show what can't be hidden
structure	static	modular
software dependencies	depending on the respective devices and manufacturers	ESPHome and Home Assistant (both also open source)
reparability	hard	very easy, everything is open source (software, hardware, knowledge (including plans)), spare parts are easily available (if you want to, you can also print them on your own) and you can also modify the TVS, personalizing it to your needs
quality	high, manufacturers having many years of experience in most cases, it will probably work fine	lower, likelihood of it to work is low, because we aren't a big, specialized company, we don't have the expertise needed, we are just trying things out and doing our best

So the TVS is probably not the best idea to go ahead with, but if we still haven't managend to get you off by now, maybe you want to take a closer look at HOW A TVS WORKS and the used PARTS.