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.
80 Year Paybacks? Is that Sensible?
September 6, 2009
Last week I again had the pleasure of renewing my acquaintance with one of the most progressive, practical builders I have encountered. It is pure pleasure tapping his brain power. I am forever amazed at how much knowledge he has regarding energy efficiency in building and his utilization of building systems in his pursuit of cost justified, profitable construction of sustainable, energy efficient building. His name is Duncan McFarland and he builds with Structurally Insulated Panels in the area of Wintergreen,Virginia I think the one issue that he and I totally agree on is: Builders have to make a profit building energy efficient/sustainable housing. That builders have to understand the costs involved, make rational decisions regarding these costs, so as to make a profit when employing energy saving/sustainable building techniques. It has to be a cost vs. value vs. profit decision. It also means that not only does a builder have to understand the costs involved, but has to communicate and educate his buyers to the advantages of having houses built this way. Usually these advantages are related directly to cost savings, putting money in the buyers pocket, and healthy/comfortable living environs.
One issue Duncan brought up was cost effectiveness of heating and air conditioning systems in a home built to tight thermal envelope standards. These standards usually involve the correct installations of windows, doors, insulation, air barriers, drainage planes and HVAC systems.
When he talked about the cost differences involving the upgrading of equipment from the old 10 SEER standard to the new 13 SEER requirements, the cost effectiveness was dramatic. He explained that upgrading to a 13 SEER Heat Pump can run approximately $4000.00 from the previous 10 SEER system. The 10 SEER system had been costing approximately $50/month to operate. The savings from installing a new 13 SEER unit into a new EarthCraft/Energy Star home, the type he had been building, were about $4/month. That is a pay-back of approximately 83 years. Now how do you sell that to a homeowner or builder.
Of course today 13 SEER is mandatory. The point is in an existing house or a new house being contemplated by a builder, upgrading the Compressor/Heat Pump unit, with a leaky thermal envelope and duct system is throwing money away. Only those with deep pockets and “Green at any cost” can justify a payback of 83 years.
The point here is it is all about a building and houses systems operating together as a team. Do a thermal envelope and HVAC supply system correctly and the effects of the efficiency of a new upgraded component are minuscule. The same holds true for installing a high efficiency HVAC unit into a leaky duct system. What are you going to save by upgrading to a 13 SEER system if your ducts leak 15-40%(not abnormal). Can anyone justify spending $4000 to save $4/month? Not in my world.
This substantiates what I have always believed. Builders, Developers, Affordable Housing producers, home-buyers and building owners are better off spending their money cost effectively on upgrading their thermal envelopes and duct systems, with the resultant instantaneous savings, reasonable payback times, then they are by jumping ahead to the glamorous, expensive, big ticket items of higher efficiency HVAC systems, windows and doors. The home buyer has to see the savings and the builder has to see the profit. How can that happen utilizing the above scenario?