I’m gonna be doing some major remodeling. I’d like to keep my existing HVAC system which is oversized for my leaky house. I plan on using spray insulation and really tigtening the house, while adding another 1600 sq ft (existing house is 2500 sq ft). But like I said, it’s got some pretty big loads on it which I plan on doing something about.
So my question is…what kind of person do I call to do a real heat loss calc. I’d also like to do a blower door test to make sure I’ve sealed up the house like I think I have. I don’t want some HVAC guy out here with basic rules of thumb trying to sell me more equipment. I want somebody that has nothing at stake other than doing the calculation.
-MERC
Replies
Might be difficult to locate someone to perform just a heat loss calc for a pure service fee. Try folks advertising "energy audits" or "weatherization contractor". Whoever performs the blower door test should be capable of this, and there would be no 'conflict' if they were not heating contractors.
If you want to figure it out yourself, you can buy this software for $50.
http://www.heat-loss.com/main.asp
Free rough online calculator:
http://hearth.com/calc/roomcalc.html
Good howto link:
http://www.diydata.com/planning/ch_design/example1_imperial.htm
My company is sort of like you describe - we get paid to do energy studies, we don't stand to gain or lose anything based on equipment purchases. However, we focus on commercial and industrial customers, not residential.
Depending on where you live, your utility company might pay for an energy audit that would offer tips on how to save energy, and potentially size HVAC equipment.
If you are relatively proficient at spreadsheets such as Excel, it's not that big of a deal to set up a model of your house that would tell you what to expect for energy use.
As you allude to, a big component is infiltration, and a blower door test would probably help. But you could also build a model of the existing building, looking at conduction and infiltration / ventilation. The conduction part is not that hard to get right, assuming you know the construction of the house. Then calibrate the model to your existing fuel / electric bills, and you can get a sense on what is due to infiltration. You might also want to get weather data (available online) to figure out how heating degree days and cooling degree days affect your consumption.
Anyway, I would check with your util co first. In Massachusetts, I am pretty sure you can get a residential audit for free.
Edited 10/7/2003 1:49:59 PM ET by AlecS
You can snoop around through the Energy Star program to maybe find some people who can help. http://www.energystar.gov/index.cfm?fuseaction=expert_help.showExpertSearch
I had an HVAC installer-sales guy I had gotten to know do a heat and cooling load on our house. Told him I was not currently in the market for a new system, but with 25 years on one heat pump, I wanted to be sure of size ahead of crunch time.With improvements we had made, I didn't want to play the replacement-in-kind game.
He came over one evening, and we put everything into his laptop. We fed him dinner, had a good time, will call him when in need. Offered to pay for his time, he refused.
To check real world against theoretical, I took a number of no heat no cool months and recorded ele and gas usage. I then subtracted these "base" months from some "heat" months and calculated the Btus I had used, for the heating degree days for that period. Results were very close when adjusting for the degree days. One of the biggest unknowns is the actual wind load, rain and clouds which can have a huge impact, so the comparitive results I got from laptop vs actual could be dumb luck.
There is a weather history web site (don't know the url, may have "subject searched" at cooling deg days) that will give you the degree days history for a given city on a daily basis. I remember adding up the day figures for each month.
What I see in most houses is a huge surplus of heat capacity, like 200%. But,as you know, it's the overkill in cooling capacity that gives poor performance, poor comfort and high operating cost.
If you tighten up the current 2500 sq ft, and build the additional 1600
using a layer of spray foam (best bang for buck is 1/2" to 1" foam, with batt behind it), I believe you can use an on-line program to get within the equipment size increments. I also think your educated guess will be just as close in the real world.
If you add an air handler, I would recommend a variable speed, which gives you more flexibility in the match-up.
Regardless of values plugged into a program, life style and unknown variables for the actual house sitting on the actual lot are wildcards
that don't compute.
If you tell me more about the system you have now, where you live, how extensive a remodel to the existing house,I may have some suggestions that will help you land within the fine tuning range. Paul
Practical Energy Cost Reduction for the Home
DJ:
Do I rember correctly that you live near Raleigh? If so, these guys will do it for you:
http://www.advancedenergy.org
actually, they will travel too, but I would think that could get expensive.
Thanks for the input. I live in Chapel Hill. I'll check them out.