Water is an extremely important factor for maintaining a comfortable house, and yet almost every home designer ignores water effects on house comfort and energy. Modeling and monitoring water movement through a house is complex and tedious, but essential. Mismanagement of water and water vapor leads to poor indoor air quality, discomfort, degradation of building materials, growth of molds, mildew and fungi with air that is too humid, and dry, itchy skin and bloody noses from excessively dry air.
Newell Instruments has developed a water transport, absorption/adsorption, and desorption process model in order to understand the impact of water (read about some of our simulation technologies and services in our Residence Engineering section). As people occupy a house, they humidify it through their metabolic processes and from their activities (aquariums, plants, showering and cooking). The model allows us to predict and understand the moisture handling processes that must be integrated into a house. In a super insulated, super sealed home, it may be necessary to dehumidify the house in the winter….quite the opposite of the humidification required by more conventional homes. Dehumidification has a much different impact on the energy balance of a house. When you humidify, energy must be added to water in order to vaporize it. The energy for a humidifier often comes from the air, chilling it and giving occupants a cold feel. When air is dehumidified, energy is released from the condensing water vapor, which in turn warms the surrounding air, leading to a more comfortable surroundings.
One of Equinox House’s most unique properties is its ability to absorb a lot of moisture. As discussed in the thermal mass section, Equinox House is a very “massive” house. In addition to being thermally massive, Equinox House also has an incredible ability to absorb moisture. The plot below shows results from our experiments to quantify the “moisture mass” of Equinox House. We have found the moisture mass is 18kg of water per % relative humidity change. That is, Equinox House will absorb 360kg (~100 gallons) of water if it were to change from 40 to 60% relative humidity.
This moisture storage characteristic coupled with Equinox House’s CERV system that can adjust fresh air ventilation rates when desired, gives Equinox House the ability to absorb a moisture punch without much ado. If you have ever had a lot of people in your house, you may have experienced water dripping down your windows in an overheated room. Most likely, someone had to open doors and windows to keep the air fresh as well as try to keep temperature and humidity in control. The plots below show data from our winter Solstice Open House Party in which over 100 friends came to celebrate Equinox House and the future of solar powered living. The open house started at 5pm, with the house rapidly filling with guests, peaking at 7pm, and then dwindling from there until at 9pm, when only a dozen or so remained. We increased the CERV’s ventilation schedule to 100% fresh air during the party(under normal living, we maintain a 1 hour out of every 3 hours of fresh air ventilation for a schedule that follows ASHRAE 62.2 residential fresh air ventilation standards). The humidity and temperature rose rapidly, but did not reach uncomfortable levels (but for sure would have with a longer party…that was a lot of people!). Between the fresh air ventilation system and the house’s energy and moisture capacitances, the house rapidly returned to normal comfort levels after the party. We were able to retain much of the human energy in our storage mass, contributing to the house heating. We’ve calculated that 20 people is sufficient to keep us comfortable on the most bitter cold day of the year. Kind of an interesting thought…conditioning your house with people.
Psychrometric instruments and old refrigeration and air conditioning books in the “historic” corner of Newell Instruments laboratory.
Closeup view of a horse hair humidity sensor/actuator. As humidity increases, hair shrinks, causing the hair to pull an actuator for some operation. Hair has been replaced by polymer fibers that have similar characteristics.
Relation between water absorbed in Equinox House and the indoor relative humidity.
Relative humidity in the main living area of Equinox House during the Solstice Party held on December 21, 2010. Over 100 people attended the party, with an estimated 80 people continuously in the main living area for two hours of celebrating solar powered living.
Temperature in the main living area of Equinox House during the Solstice Party held on December 21, 2010. Over 100 people attended the party, with an estimated 80 people continuously in the main living area for two hours of celebrating solar powered living.
