Suggestions for New Construction in High Humidithy Area?

[teddy bear]

Thanks TB, but I believe that this approach is incompatible with the well-being of the occupants. It's been found that low absolute humidity (dew point) increases virus transmission (not relative humidity). Below about 15 mbar of water vapor pressure, the influenza virus greatly increases its survivability and infection rates (see "Absolute humidity modulates influenza survival, transmission, and seasonality", Shaman and Kohn 2009, Proceedings of the National Academy of Sciences, http://www.pnas.org/content/early/20....full.pdf+html). That's a dew point of about 55^F. Air with less than a 50^F dew point is a health issue, besides causing discomfort. Recommending increased ventilation to reduce the dew point down below 32^F dew point or less in winter is risky for human health.

Interesting, who is going to tell all those people in the more arrid climates?
I suggest that mold free is healthier than a high indoor humidity in the winter time. Most of the discussion is about 70^F, 50%RH verses 30^F 50%RH.

"Recent theoretical work has shown that slight seasonal
changes in transmission efficiency can produce the strong seasonal
cycle in influenza incidence through dynamical resonance
(21). The findings presented here indicate that the seasonal cycle
of AH may be the factor producing this resonance. Specifically,
low wintertime AH levels, both indoor and outdoor, increase
influenza IVS and thus increase IVT efficiency.
These findings also suggest that humidification of indoor air,
particularly in places where transmission to those at high risk for
complications, such as nursing homes and emergency rooms,
may help decrease the spread and the toll of influenza during
influenza season. Previous studies using RH (8–10, 13–19, 22)
also supported similar air humidification practices; however,
these assertions were perhaps undermined by the marginal
association of RH with IVS and IVT. Our findings, which
attribute a much stronger effect of AH on both IVT and IVS
(Figs. 1 and 3), suggest that humidification measures may be
warranted."
Most suggest that after getting adequate fresh air to purge indoor pollutants, humidify to just below the point of condensation on the cool surfaces. No problem for me. Humidification to the point of growing biologicals like mold and dust mites is not suggested. Normal temperatures indoors and 50%RH is comfortable. The coldest climates will occasionally require 35%RH to avoid condensation. What has research on the effect of inadequate fresh air change on occupied space suggests high pollutants and virus concentrations? I assume not good.
Regards TB

[pmeunier]

TB, Isn't it possible to have, with the right equipment and building, healthy humidity, fresh air and no mold? I hear you about the customer that was "out of money", it may not be possible to have all 3 and a choice needs to be made. However, is it really extravagant to want all 3?

[teddy bear]

TB, Isn't it possible to have, with the right equipment and building, healthy humidity, fresh air and no mold? I hear you about the customer that was "out of money", it may not be possible to have all 3 and a choice needs to be made. However, is it really extravagant to want all 3?

It depends on "healthy humidity, fresh air and no mold" is. Healthy humidity is the part needs clarification. I fell that 40%RH winter and 50%RH for the summer is healthy. This is doable with some form of mechanical ventilation, a humidifier, and a dehumidifier. High quality windows and a moderately air tight structure are part of the equation.
Regards TB

[kaleun]

Interesting, who is going to tell all those people in the more arrid climates?
I suggest that mold free is healthier than a high indoor humidity in the winter time. Most of the discussion is about 70^F, 50%RH verses 30^F 50%RH.

"Recent theoretical work has shown that slight seasonal
changes in transmission efficiency can produce the strong seasonal
cycle in influenza incidence through dynamical resonance
(21). The findings presented here indicate that the seasonal cycle
of AH may be the factor producing this resonance. Specifically,
low wintertime AH levels, both indoor and outdoor, increase
influenza IVS and thus increase IVT efficiency.
These findings also suggest that humidification of indoor air,
particularly in places where transmission to those at high risk for
complications, such as nursing homes and emergency rooms,
may help decrease the spread and the toll of influenza during
influenza season. Previous studies using RH (8–10, 13–19, 22)
also supported similar air humidification practices; however,
these assertions were perhaps undermined by the marginal
association of RH with IVS and IVT. Our findings, which
attribute a much stronger effect of AH on both IVT and IVS
(Figs. 1 and 3), suggest that humidification measures may be
warranted."
Most suggest that after getting adequate fresh air to purge indoor pollutants, humidify to just below the point of condensation on the cool surfaces. No problem for me. Humidification to the point of growing biologicals like mold and dust mites is not suggested. Normal temperatures indoors and 50%RH is comfortable. The coldest climates will occasionally require 35%RH to avoid condensation. What has research on the effect of inadequate fresh air change on occupied space suggests high pollutants and virus concentrations? I assume not good.
Regards TB

humidifying to "just under condensation" is difficult with many thermal bridges as you have in buildings. And this also means you will be right under 100% RH at the perimeter wall. Some air also goes inside the wall where it is even colder. (that's why ASHRAE recommends negative pressure in winter, positive in summer... most designers just make it positive all year).

And focusing on just influence virus is a problem when that ignores all the other issues (look at ASHRAE humidity/bio growth chart). I'm not a doctor, but influence happily spreads from human to human without much need to be in the (artificially humidified) building. and higher humidity may grow even worse other bugs. In winter everyone is just exposed to influenza, you can't sterilize the world.

Humans lived in outside air for thousands of years and can take it. Now when we live in buildings, we create artificially more humid environments (since we produce water). Keeping it naturally more dry seems more healthy and natural to me. the people in arid winter areas like Colorado never seem to have a problem with that.

[unc99]

TB and others, a few additional questions if you don't mind:

1. If I put a venting dehumidifier on just one floor (ie, either in the crawlspace or attic for a two story, two unit home), would it be the first or second floor?

2. Could I put an ERV on on floor and a venting dehumidifier on the to other floor? Maybe this is overkill, but just thinking through all options.

3. Should I get a variable speed HVAC or regular?

Thanks!

[kaleun]

TB and others, a few additional questions if you don't mind:

1. If I put a venting dehumidifier on just one floor (ie, either in the crawlspace or attic for a two story, two unit home), would it be the first or second floor?

2. Could I put an ERV on on floor and a venting dehumidifier on the to other floor? Maybe this is overkill, but just thinking through all options.

3. Should I get a variable speed HVAC or regular?

Thanks!

1. If you really need a dehumidifier, put it in the lowest floor since that usually is colder and the dehumidifier adds heat (all the electricity it uses ultimately becomes heat plus the latent heat of water vapor)

2. I don't see a reason for an ERV going from conditioned to just slightly differently conditioned space

3. Variable speed will dehumidify better (if same total size), be more efficient under partial load and will wear out less due to less cycling. so yes to that. In residential you mostly get a 2 or 3-speed compressor, for example the "Carrier Infinity 21". Some other forum member have more knowledge on specific models than I do.