To enable positive perceptions of thermal
comfort.
To enable positive perceptions of indoor
air quality and respiratory comfort.
To enable positive perceptions of indoor
odour quality.
To enable comfort in mucous membranes.
To control hydrolysis (VOC emissions).
To control microbial.
To maintain dimensional stability in
hygroscopic materials (woods).
To prevent condensation on hydrophobic
materials (glass, aluminum).
To prevent condensation in hydrophilic
materials (drywall).
To preserve moisture sensitive artifacts
/ collectibles / musical instruments.
Split whole house ventilating
dehumidifier with no added sensible heat load —
specifically designed for hot, humid climates.
What does Dr. Stephanie Taylor, M.D.,
M. Arch, CIC have to say about controlling temperature
and humidity?
"Physicians are aware that indoor
climates of 70˚F to 72˚F with 40% to 60% rh decrease
respiratory infections, promote wound healing, and
decrease dehydration from transdermal water loss. This
is well established! Extensive research done by the
military also shows that our skin coefficient of
elasticity (Young’s modulus and shear strength) are
determined by skin hydration, skin temperature, ambient
temperature, and air humidity. Dry climatic conditions
worsen skin inflammation and decrease essential barrier
functions that protect underlying tissues from
mechanical stress damage, skin irritants, and
allergens."
Recently I was enroute to Halifax, NS to deliver
a lecture on
thermal comfort to the
Nova Scotia Home Builders
Association. Scheduled along the way I dropped into Madison,
WI to participate in an appropriately tagged, “moisture mind
meld” with a brain trust of humidity experts.(1) You might ask
where a bunch of building geeks would hold such a meeting. Well
in a State home to my paternal grandmother is the home of an
enthusiastic American manufacturer of some of the best
engineered dehumidification equipment made on the continent.
Building folks know them under the brand of
Therma-Stor and their
ingenuity is found all over the world and in many devices used
in conditioning people and spaces and in the building
restoration and maintenance industry.
So why the get together?
That’s where Nikki Krueger, Industry Manager for Therma-Stor, and engineers
Andy Ask and Tim O'Brien
(Business and Product Development) enter the
story.
Therma-Stors’ team flew several times onto my
radar screen over the past few years at the Building Science
Summer Camp hosted by Joe Lstiburek, Ph.D., P.Eng. of
Building Science Corporation fame, then the Better Building
Better Business Conference run by
Seventhwave followed
by the
Humid Climate Conference in partnership with the Passive
House Institute (Austin Chapter).
Seems fate was at work again because for the
past few years I have also been studying moisture challenges in
buildings including health effects on people and debunking the
myth that condensation was the root of all evil in
radiant cooling systems.
Funny how when there is a need to elevate an
important message to society that a greater power manages to
bring together those who can make a difference. Well the round
up which included engineers, scientists and builders like
Kristof Irwin, M.Sc.,
P.Eng.,
Allison Bailes, Ph.D.,
Armin Rudd,
Chris Conway and
John
Semmelhack, was the work of Ms. Krueger. Nikki works with
two visionaries in the industry, that being President Todd
DeMonte and the legendary Ken Gehring. Gehring, affectionately
known as Teddy Bear, invented the Ultra-Aire whole house
ventilating dehumidifier back in 1996. If you need to know anything
more about Todd and Ken is that they
with their team, raised the company to the success story that it
is today. Along with Nikki, Therma-Stor hosted the humidity event in part for the purposes of
identifying how industry can do a better job of educating the
home buyer and house building industry on the benefits of
controlling moisture with simpler more effective solutions. A
fundamental principle I fully endorse.
We discussed a lot of stuff that day but much of
it boils down to this; as buildings become more energy
efficient, their sensible cooling loads go down and that drives
up the relative importance of moisture loads due to the ever
present constants of occupant behaviour and ventilation air.
There is a similar result with below grade heat losses having a
greater consequence on total loads when above grade walls and
roofs enclosures are improved.
So what does this mean?
It means people installing whole home A/C systems
for thermal comfort in high performance homes with the assumption that effective
dehumidification will occur, could be sadly disappointed as
compressors cycle down or off due to the low and infrequent
cooling comfort loads especially associated with shoulder
seasons. Those shoulder seasons in the eyes of the mechanical
system become longer as home performance increases. The result
of low load homes is exacerbated further with oversized systems
which regrettably is a systemic problem in the HVAC industry.
Consider, in absence of smaller dedicated dehumidification
systems, when the blower in the primary HVAC system is
“off” as controlled by a thermostat, there is no air
recirculation, no introduction of ventilation air, no filtration
and no dehumidification. Herein lays the problems and why
companies like Therma-Stor are positioned nicely as experts in
the growing dedicated dehumidification solutions business. You see with these dedicated
systems and if necessary, strategically selected and positioned
in-space fans (ceiling, desk or floor mount);
people can enjoy drier, cleaner and more thermally comfortable
rooms. It also means people who want to
use radiant cooling in homes can do so with a dedicated
system. This ought to make the PEX pipe folks very happy because
it simplifies the design process and it fits so well with the
ethos of comfortable and efficient radiant cooling systems.
Check out Matt Risingers
coverage of Therma-Stors SD12 unit. Matt has a great way of
explaining why these stand-alone systems work so well.
Following our meetings in Madison and with
additional input from physicians and industry engineers, I’ve
revised my position on moisture control as noted below.
Beans’ Ten Best Reasons To Control Relative
Humidity Between [35% and 55%] +/- 5%
1. To enable positive perceptions of
thermal comfort
The authoritative document governing thermal
comfort is ASHRAE Standard 55 Thermal Environmental
Conditions for Human Occupancy. The DNA for compliance
includes ten prime metrics of which controlling humidity in
one of them. To see the effect of humidity, readers are
advised to visit our comfort simulator at
http://www.healthyheating.com/solutions.htm or the CBE
Comfort tool at http://comfort.cbe.berkeley.edu/
.
Figure 1. Thermal comfort zone
using the ASHRAE graphical method incorporates humidity and
operative temperature (for larger images and more detail
see our
ASHRAE San Antonio Presentation note: you'll need the
password - simply join our
Linked-In discussion group and request the password - be
sure to provide the URL of the presentation page).
2. To enable positive perceptions of
indoor air quality and respiratory comfort
Research by Berglund and Cain (1989) and Cain
et al. (1983) showed decreasing acceptability of air quality
with increasing air temperature and humidity. Toftum (1998)
showed that humidity controlled between 30% and 60% resulted
in the least amount of occupants dissatisfied at a nominal
68°F (20°C). As temperatures increased for example to 72°F
(22°C) occupants preferred humidity controlled between 30%
and 40%. The challenge here is physicians would prefer the
higher values (40% to 60%) but to do that the temperature
would need to decrease. In traditional homes with high
summer time MRT’s lower setpoints require energy for
mechanical cooling; but in high performance homes with lower
summer time MRT’s and with lower humidity, elevated air
speeds achieved with ceiling fans can be used instead.
Figure 2. Upper limits of air humidity for
preventing warm respiratory discomfort
Figure 3. Human satisfaction with the indoor
air quality depending on relative humidity and air
temperature.
3. To enable positive perceptions of
indoor odour quality
Fang et al (1999) noted the effect of
humidity on chemical and sensory emissions from building
materials was found to be significant for waterborne
materials such as floor varnishes and wall paints. In
balancing between respiratory preferences and odour quality
it is recommended to maintain humidity levels as prescribed
towards the lower value and choose appropriate interior finishes.
4. To enable comfort in mucous membranes.
A healthy body is a hydrated body. When
moisture content in sensitive organs such as eyes, nose,
throat and skin is below or above optimum they become
irritated leading to both physiological and psychological
stress. For this reason moisture should not be too high nor
too low and controlled with dehumidification or
humidification as required. For further studies on effects
from high humidity see
hidromeiosis.
5. To control hydrolysis (VOC emissions)
Many building products especially interior
finishes have components which are susceptible to breaking
down into gases in the presence of a solvent such as water
vapour. Formaldehyde is one such constituent and is commonly
found in glues used in flooring, furniture and millwork.
Maintaining lower humidly levels in the home reduces the
probabilities of such lung irritants being released into the
air (Corsi, 2013).
Figure 4. Relative humidity and paint emissions
6. To control microbial
When relative humidity is controlled within
the prescribed range there is less risk of sustaining
environments which support the growth of virus, bacteria,
molds, mites, and some insects. All which can trigger
negative response systems in the body.
Figure 5. Optimum zone for
humidity (for larger images and more detail
see our
ASHRAE San Antonio Presentation - note: you'll need the
password - simply join our
Linked-In discussion group and request the password - be
sure to provide the URL of the presentation page).
Adapted:"Criteria for Human Exposure to Humidity in Occupied Buildings." Dr. Elia Sterling, 1985
and ASHRAE Handbook of Fundamentals 2013.
7. To maintain dimensional stability in
hygroscopic materials (woods)
Building scientists demonstrate that the
dimensional stability of materials such as woods are
intimately connected to space moisture content. Equilibrium
moisture content in woods maintained between 6% and 14%
corresponds to relative room humidity between [40% and
60%]+/-10% at dry bulb temperatures between 70°F and 80°F
(21°C and 27°C). Ergo when moisture is controlled both in
the wood and space, the differences in vapour pressure
between the two is minimized which mitigates the risk of
wood swelling or shrinking.
Figure 6. Maintaining dimensional stability
in woods.
8. To prevent condensation on hydrophobic
materials (glass, aluminum)
The dew point on a surfaces is a function of
its temperature and the moisture content in the air
immediately adjacent to the surface. With window and door
glass and frames exposed to cooler temperatures there is
wetting potential even with moderate humidity. The options
are to lower room moisture and/or reduce the glass and frame
conductivity. Again the physicians advise against ultra low
humidity so in colder climates it’s important to work with
the indoor environmental engineer to design the proper
combination of space moisture (towards lower RH) and glazing systems
(towards higher R value) in concert
with the window treatments and HVAC systems (those that
promote drying) so at design
conditions there will be no wetting on these inherently cold surfaces
(see #6 above).
Figure 7. Window type
performance at various humidities and outdoor
temperatures. Source:
THERM5.2/Windows5.2 NFRC Simulation Manual, Fenestration
Heat Transfer Basics, Condensation Resistance
9. To prevent condensation in hydrophilic
materials (drywall)
As above, except moisture diffuses into and
through the material, causing increasing levels of dampness
as it encounters cooler conditions.
Figure 8. Vapour pressure differentials drive moisture down
a gradient into and through vapour permeable materials. When
moisture reaches the dew point on a surface, condensation
will occur.
10. To preserve moisture sensitive
artifacts / collectibles / musical instruments etc.
There is no shortage of study in preserving
moisture sensitive items such as photographs, literature,
musical instruments, paintings, wood carvings and furniture.
Damage or material stress can occur frequently when these
items are transferred from one environment to another having
a different relative humidity; or when moisture levels are
left uncontrolled. Since not all artifacts use the same
preservation approach it is important once again to work with
the indoor environmental engineer to ensure the space
conditions are suitable for the items of concern.
Figure 9. Preservation of photographs based
on recommended values from the Image Permanence Institute.
Note the lower RH range.
So there you have it, ten very good reasons
why you should be controlling your humidity between [35% and
55%] +/- 5%. When you do this in conjunction with elevated
air speeds from fans, you can in many cases reduce or
eliminate traditional and energy intensive A/C systems; or
at the very least optimize its' design and operation. It
also opens up the use of radiant cooling systems known for
their comfort and efficiency.
1. Moisture mind meld is the tag by Kristof
Irwin from Positive Energy
To enable positive perceptions of thermal
comfort.
