Handling Humidity Report Series
At Build Equinox, we have always included moisture management as a primary aspect of CERV2 smart ventilation design. Our free-to-use ZEROs (Zero Energy Residential Optimization software) model is one of the few residential programs that can predict dehumidification and humidification in residences. Health, comfort and energy impacts of humidity are important! Moisture is complex and has many facets, however it is an old, old problem that experienced HVACR engineers know how to address.
This report series discusses sources of moisture in homes (Part 1), climate impact on a home’s moisture management requirements (Part 2), moisture management methods (Part 3), and overall house modeling of moisture and energy (Part 4). Part 1 is available from our website now. Part 2 will be posted with our September 2019 newsletter, followed by Part 3 in October 2019, and Part 4 in November 2019.
Read a sample from part 1 below, or view the full report
The first building air conditioning system (see Figure 1) was designed for moisture management, not cooling. A young engineer named Willis Carrier designed his novel air conditioning system to reduce building humidity, allowing a printing business to operate during New York City’s muggy summers. Many people are surprised to learn that Carrier dehumidified the air by spraying water into it! How can you dehumidify air by spraying water? The answer is a good understanding of thermodynamics.
Carrier’s next project was on Wall St where investors knew that improved comfort would increase employee productivity, and that increased human productivity meant increased profits. Human productivity is significantly impacted by air quality and comfort, and human productivity is 100 times more valuable than the energy required to maintain a healthy, comfortable indoor environment.
Table 1 below shows daily moisture additions to a home from occupants and their activities. Part 1 dives into the background for determining human moisture impacts on homes.
Infiltration and ventilation are two additional factors affecting a home’s moisture balance. Figure 2 (below) shows the infiltration air flow for a 2000ft2 home with a volume of 16,000ft3 (8 ft high ceilings). A leaky home with 6ACH at 50Pa has a flow of 140cfm with an average wind speed of 7 to 8 mph in contrast to a 0.6ACH at 50Pa, well-sealed home with 14cfm infiltration.
In Part 1, we examine Contractor Loose, Contractor Tight, and Contractor Smart construction characteristics. These contractors are building 2000ft2, 3 bedroom homes in Urbana Illinois for 2 occupants who are home an average of 16 hours per day. Contractor Loose is a conventional builder who will build a 6ACH at 50Pa home while Contractor Tight’s more advanced construction methods produce 0.6ACH at 50Pa homes. Both Contractors Loose and Tight ventilate with high efficiency HRVs at ASHRAE 62.2-2016 levels (90cfm). Contractor Smart also builds a 0.6ACH at 50Pa sealed home, but uses a smart ventilation and smart air distribution system, ensuring healthy air when and where needed by the home’s occupants.
In Urbana’s muggy summer weather, Contractor Loose’s home requires an average dehumidification of 37liters (78pints) of water per day. Contractor Tight’s home must dehumidify an average of 18liters (38pints) per day. Most of the water in Contractor Tight’s home is from ventilation. Contractor Smart’s home has an average summer dehumidification capacity of 6.5liters (14pints) per day.
Contractors Loose and Tight may need additional dehumidification capacity to handle Urbana’s summer moisture loads while Contractor Smart’s summer dehumidification loads can be managed with a 1 ton minisplit, CERV2 smart ventilation heat pump, and the home’s heat pump water heater.
It is important to note that Contractor Smart’s sealed, smart ventilated home has better air quality than Contractor Loose and Contractor Tight homes, even though Loose and Tight home’s have much higher ventilation and infiltration air flow rates. Poor fresh air distribution results in inefficient use of fresh air. Leaky homes and tight, overventilated homes are not homes with good air quality if air distribution within the home is poor.
Equinox House (figure 3) was sealed to 0.5ACH at 50Pa in 2010, and has 2100ft2 for floor area with 2 occupants. Historical data (CO2, VOCs, temperature and humidity) from Equinox House can be viewed online from 2014 to present (visit BuildEquinox.com, and scroll to the “Take Control” section). Equinox House never sacrifices comfort and always has excellent air quality.
Figure 4 shows wide variations dehumidification capacity on a day-by-day basis, with some days requiring 20 to 25 liters of dehumidification while other days have none. Warm, humid weather and occupant activities both cause wide swings in dehumidification requirements. Overall, the 5 to 6 kg per day of condensate collection is in agreement with Contractor Smart’s Urbana home. Dehumidification capacity variations in Contractor Loose and Contractor Tight homes are much greater and likely to cause periods of discomfort as well as high energy usage.