Too Much Heat and Moisture in an Energy Efficient New House.
February 15, 2010
In my last posting I was dealing with a real life building issue of condensation on the rim band of an insulated, pressurized crawl space. So who cares, it is in the crawl space. Well that is what causes mold, rot and unhealthy living conditions.
Many people would say, “See we been telling you are making houses too tight causing other issues and problems.” You Green, tree hugging builders are causing us more problems. In a perfect world that could be argued as true. There is one difference today, “energy ain’t cheap,” and it is destined to get less real cheap quickly. But I will deal with that thought in another post.
The crawl space was insulated with an R-10 Thermax Insulation Board. The Rim Board is insulated with R-19 fiberglass insulation. There is a vapor barrier covering the entire floor, no gaps. There is a HVAC supply duct providing heat to the crawl space and keeping it under a slightly positive pressure. This keeps a crawl space from sucking in exterior moisture from the ground. If we have all of this stuff place how do we end with a moisture problem?
Here’s the actual conditions on site: The contributing pieces of the puzzle:
In the main body of the house the thermostat is set on 77 degrees. The outside temperature is about 28 degrees and the wind is howling. The interior temperature is 72 degrees. The relative humidity is 92%.
Using a sling hydrometer it was determined that the dew point is roughly 82 degrees. It should be raining in the house. The house feels like we should be drinking Margaritas and sitting on the beach in the Yucatan Peninsula.
When the front door is open and the storm door exposed, it immediately fogs up like a mirror after a hot shower. The windows have moisture condensing on them, even though they are insulating glass. In the crawl space the same conditions exist, as we have the referenced pressurized, conditioned crawl meaning a supply duct delivers the same air to the crawl.
When we pull the R19 fiberglass insulation off the rim boards, Walla, they are soaked with water, and the temperature on the rim is 44 degrees. Way below dew point of 82 degrees. We have a problem, what is causing it and do we have any solutions? We better have.
I had a similar problem about a month ago in a newly renovated affordable housing project. The project was completed to EarthCraft Green Building renovation standards, which basically requires the improvements get the Air Changes per hour below .6 and a 30% improvement over the original, pre-renovation energy conditions. I had inspected the work as it was being completed. Yet a couple months after occupancy I was being called by developer wondering why they had an entire wall with moisture running down it. This was meant to be an energy efficient renovation.
What do I find, again a wall temperature in one corner of about 40 degrees, as an outside water spicket, unique to this one unit, hasn’t been sealed and all that cold air is condensing the hot moist air from the heating unit on the inside. The outside wall, which is about 16 feet long and 8 feet high has water rivulets dripping down and the Sheetrock is saturated from the floor to about 3 feet above it. As I move the temperature gun away from the spicket area and the floor, moving up the wall the Sheetrock starts to heat up rapidly from below 40 to above 60 degrees about 3 feet up the wall, where the condensation stops. I know this outside wall, it is an end unit, is brick, but it had been re-insulated, what is causing this problem?
When I went back to check in late April, the wall, due to the Western Sun finally hitting the wall, had heated up and signs of condensation had disappeared on outside of wall.
Tight Houses cause Water and HVAC design concerns.
February 11, 2010
Two real life, on the ground, issues have me concerned both as a builder and purported Hi-Performance, Energy Efficient design consultant.
1. In pre-planning a Structurally Insulated Panel(SIP) condominium quadruplex there are practical heating and air conditioning problems to be solved. Do you use time tested conventional approaches or install evolving HVAC equipment?
This building’s thermal envelope(exterior shell) is so energy efficient and tight that the HVAC load requirements for each unit(950 SF) are below that of the smallest sized, readily available, cost effective, conventionally ducted HVAC equipment. This means the conventional unit is oversized, a no-no in High Performance housing.
A readily available, 16 SEER, 1.5 ton Heat Pump is almost double the size necessary to heat and cool these units. The problem isn’t about being able to heat and cool the unit. It is how do you remove the interior moisture(humidity) consistently? An oversized unit runs in short spurts and every time it stops, dehumidification stops. The solution is either utilizing the new mini-split, inverter technology units or adding a dehumidification system to the conventional unit. The decision has to be based on performance and cost. Stay tuned.
2. A group of affordable, energy efficient houses were built with conditioned crawl spaces and a super tight building envelope. The houses have developed condensation/moisture issues on the interior of the homes. The homes were built with no design input from experienced Green Builders or real world Hi-Performance home consultants. They were not Energy Star Certified, so there were no third party Hers Raters involved. This type of problem is caused by the theory of, “Make the house tight, and forget about evaluating other issues that have to be solved in designing a tight, Green Home.” Stay tuned for solutions.
The theory to reality application is going to present issues now and into the future, as more and more builders, designers, etc. jump on this believed economic windfall Green job wagon. Many so called experts are Tin Men, just selling stuff, not economic, practical solutions.