3 ms·

Am I reading this right? Is there no heat exchanger in the ventilation? That seems like an obvious improvement.

vesinisa 3y ago
The ventilation within the sauna is actually more effective the greater the temperature gradient between the entering low-CO2, cold air and the stale, hot air in the sauna. You want the entering air "falling" on the stove because it's colder i.e. denser than the surrounding air. It then heats up and mixes with the hot air in the sauna. That being said, almost any real implementation in a cold climate place like Finland would have a heat exchanger at the building level for a mechanized ventilation system. It's of course still not 100% efficient so the circulation system within the sauna still works.
- Ekaros 3y ago
  Also to remember is that amount of moisture added in usual sauna session is not insignificant. Throwing at least couple of litres of water on stove is entirely normal in addition to whatever is perspired. Handling this level of possible condensation might need additional considerations.
- Thorrez 3y ago
  What does "at the building level" mean? Is the sauna only part of the building and not the whole building? The article says it's a backyard sauna, which to me sounds like the sauna is the whole building.
  - distances 3y ago
    Can't speak for this article, but an electric sauna in Finland is almost always inside the building/apartment, accessed via the bathroom. A separate sauna building would have a wood heated stove.
  - vesinisa 3y ago
    Depending on configuration, either on the apartment unit, single-family house or apartment building level. As the other commenter said, nowadays sauna in Finland is usually inside your house and the mechanized ventilation is connected to the overall ventilation system of your house. Hence the original article[1] explored the optimal positioning for mechanized air in/outlets in a sauna. The current Finnish building code incorporates the recommendations from this study (as document RT 91-11260). I guess you could apply the same principles to an electric sauna in a separate building. Just use two fans (one pulling, one pushing) instead of an AC system. Most often a separate sauna building in Finland however has a wood-fired stove, which doesn't need as much consideration for ventilation as an electric sauna. My understanding is that the wood-fired stove itself creates a strong continuous draft which takes care of ventilation in the sauna room (pulling fresh air from outside through the stove and by combustion into the chimney). [1]: https://publications.vtt.fi/pdf/tiedotteet/1992/T1431.pdf https://publications.vtt.fi/pdf/tiedotteet/1992/T1431.pdf
Maxion 3y ago
I'm not really sure what you're critizisng? This was a study done in the early 1990s looking at what would be the best way to build a sauna. This isn't a study in HVAC optimization for a house. FWIW current finnish building code more-or-less require a heat exchanger in the exhaust air flow. It didn't in 1990.
Aurornis 3y ago
A sauna is a small, enclosed area with an extremely high moisture content that is only used for short periods of time. The expense of a heat recovery ventilator that could work with this extreme level of moisture wouldn’t even come close to recouping any potential cost savings. The combination of ventilation and heat source along with water poured on to the source is a way to regulate and adjust the temperature. The goal isn’t to trap as much heat as possible because having some of the heat flow out is key to regulating temperatures. So, not really an obvious improvement at all.
- lukan 3y ago
  "The goal isn’t to trap as much heat as possible because having some of the heat flow out is key to regulating temperatures." Rather to get old air out and fresh one in. Temperature regulation is done by more or less heating, or if all fails, opening the door.
- SoftTalker 3y ago
  Dry saunas are a thing also. My gym sauna is dry except for the humidity provided by the sweating people sitting in it. They prohibit putting water on the rocks.
  - yencabulator 3y ago
    Sure but that has very little to do with the Finnish designs of saunas.

The ventilation within the sauna is actually more effective the greater the temperature gradient between the entering low-CO2, cold air and the stale, hot air in the sauna. You want the entering air "falling" on the stove because it's colder i.e. denser than the surrounding air. It then heats up and mixes with the hot air in the sauna. That being said, almost any real implementation in a cold climate place like Finland would have a heat exchanger at the building level for a mechanized ventilation system. It's of course still not 100% efficient so the circulation system within the sauna still works.

Ekaros 3y ago
Also to remember is that amount of moisture added in usual sauna session is not insignificant. Throwing at least couple of litres of water on stove is entirely normal in addition to whatever is perspired. Handling this level of possible condensation might need additional considerations.
Thorrez 3y ago
What does "at the building level" mean? Is the sauna only part of the building and not the whole building? The article says it's a backyard sauna, which to me sounds like the sauna is the whole building.
- distances 3y ago
  Can't speak for this article, but an electric sauna in Finland is almost always inside the building/apartment, accessed via the bathroom. A separate sauna building would have a wood heated stove.
- vesinisa 3y ago
  Depending on configuration, either on the apartment unit, single-family house or apartment building level. As the other commenter said, nowadays sauna in Finland is usually inside your house and the mechanized ventilation is connected to the overall ventilation system of your house. Hence the original article[1] explored the optimal positioning for mechanized air in/outlets in a sauna. The current Finnish building code incorporates the recommendations from this study (as document RT 91-11260). I guess you could apply the same principles to an electric sauna in a separate building. Just use two fans (one pulling, one pushing) instead of an AC system. Most often a separate sauna building in Finland however has a wood-fired stove, which doesn't need as much consideration for ventilation as an electric sauna. My understanding is that the wood-fired stove itself creates a strong continuous draft which takes care of ventilation in the sauna room (pulling fresh air from outside through the stove and by combustion into the chimney). [1]: https://publications.vtt.fi/pdf/tiedotteet/1992/T1431.pdf https://publications.vtt.fi/pdf/tiedotteet/1992/T1431.pdf

Maxion 3y ago

I'm not really sure what you're critizisng? This was a study done in the early 1990s looking at what would be the best way to build a sauna. This isn't a study in HVAC optimization for a house. FWIW current finnish building code more-or-less require a heat exchanger in the exhaust air flow. It didn't in 1990.

Aurornis 3y ago

A sauna is a small, enclosed area with an extremely high moisture content that is only used for short periods of time. The expense of a heat recovery ventilator that could work with this extreme level of moisture wouldn’t even come close to recouping any potential cost savings. The combination of ventilation and heat source along with water poured on to the source is a way to regulate and adjust the temperature. The goal isn’t to trap as much heat as possible because having some of the heat flow out is key to regulating temperatures. So, not really an obvious improvement at all.

lukan 3y ago
"The goal isn’t to trap as much heat as possible because having some of the heat flow out is key to regulating temperatures." Rather to get old air out and fresh one in. Temperature regulation is done by more or less heating, or if all fails, opening the door.
SoftTalker 3y ago
Dry saunas are a thing also. My gym sauna is dry except for the humidity provided by the sweating people sitting in it. They prohibit putting water on the rocks.
- yencabulator 3y ago
  Sure but that has very little to do with the Finnish designs of saunas.