Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation
California has again pushed their energy bar higher. One of the things that I love about California’s energy program is that they are now requiring an independent evaluation and commissioning beyond the air conditioning contractor of the sizing and installation of air conditioning systems.
Recently, I participated in a workshop with a Philadelphia-based builder. He is a very professional, conscientious builder who stays in touch with building science and education. He brought his mechanical contractor to the workshop and we had a chance to talk about the way homes are built and particularly the mechanical systems.
Here is the situation:
- There are still ‘rules of thumb’ being applied to the sizing of mechanical systems in our homes.
- Manufacturers make changes to equipment to help those ‘rules of thumb’ meet the requirements, especially regarding motors and equipment that can tune itself to the needs of the house.
What we really need are systems that are designed and installed to the actual house.
We can’t expect equipment to be continuously updated or modified to make up for our lack of willingness to do a simple calculation as to what the house really needs. It’s not just about the tonnage of air conditioning and the size of the heating units. It is mostly about the delivery – the physics of the delivery – of that comfort.
When someone tells me something regarding heating or cooling that just isn’t sitting well and I need a gut check, my gut actually lives out in Missouri and his name is Eric Kjelshus. He is a Missouri Mechanical Contractor with his own company, Eric Kjelshus Energy. He is a smart, thorough, well studied mechanical contractor who cares about this stuff far beyond anyone else I have come across.
It seems like many of the builders I have spoken with have been spending a lot of effort (effort = $$) after the sale trying to make the homes they have constructed meet the comfort expectations of the owners. This leads me to wonder if there are things we consistently get wrong with regard to how we deliver comfort. Time for another gut check!
Here is what Eric taught me:
We under return air in our homes. Very few people consistently measure static pressures in the HVAC system to find out if it is balanced. If they did they would see that the system is not returning the same volume of air it is supplying. When we under return, we force the system to pull make-up air from outside the home. Air conditioning is more efficient when the air is dry. For most of us residing east of the Rocky Mountains, the return air in our homes is both cooler and dryer than the air outside during our cooling periods. Pulling unconditioned and uncontrolled air from outside the home into the system is a big efficiency penalty and it’s one we pay for over and over again. Why not simply return the correct volume of conditioned air back to the unit? Not only is this an elegant, passive solution to the problem – it comes with a much lower up front cost than high tech solutions.
So hats off to California for requiring that trained professionals check these systems to ensure they are properly sized and installed. We as consumers can get much better value out of systems that are less sophisticated but are sized and built right.