Question from energy homeowner:

 

Contractor has recommended installing a two stage Water Furnace Envision w/desup NDV049A system into a 2700 square foot cape cod, 1000 square feet basement, 1000 square feet first floor, and a 700 square foot second floor.  The house is all brick and was built in 1950, walls and attics are currently insulated using r 11.  The blower door test gave a  2800 cfm reading at 50.

 

Contractor is recommending a 4 ton geothermal system, According to his comments it is a two stage system that  will run at 60% capacity at the first stage and 100% at the second stage.  Contractor feels the 4 ton system will provide more heat using the geothermal without going to the back up heat.,

 

If the system is over-sized to accommodate the heating season, does this make sense.?  He says with a two stage system it does.  Will the system operate efficiently.  If we were installing a regular electric heat pump the manual J test called for a 3 ton system  (single stage)   Is the contractor correct in over-sizing the unit to provide more geothermal heat in the winter months?

 

One other question: What is the advantage of using galvanized ducts as compared to 1 inch rigid fiberboard ducts?

 

Thank you for responses

 

 

 

Views: 1057

Reply to This

Replies to This Discussion

Hi my name is Steve.

If the manual J suggested a 3 ton I would look at a 3 ton two-stage. The two stage units are usually a 1/2 ton larger in size. When I size my units, I try to shoot for a balance point of 5 to 10 degrees outside temperatures here in Michigan. The operating cost seems to be the best at these temps (even with the little back up thats needed). The reason is the larger compressors use most electricity. Now, it's not a lot of difference in operating cost. Having the next size larger is not devastating but you need to have larger duct system and extra loop installed driving up installation cost.

My question is? Did the contractor you are referring to complete a manual J load and does he know where his balance points are. If he can not show you he calculations he is guessing and not doing you a good job.

Note: The home generates a certain amount of heat and you can design at 77% of the calculated load. So if the manual J says you can install a 3 ton then it does not matter if it it two stage or not. Sorry I have to go now my wife i waiting, You can contact me if you have more questions at performancegeothermal@gmail.com.

Steve Shannon

PS, I like sheet metal for duct work.

If the contractor doesn't calculate a manual J,D, and S worksheet for the house then he's merely guessing. Also, galvanized ducting last much longer, is easier to clean, and is more rigid that fiberboard.

RSS

Videos

  • Add Videos
  • View All

Twitter

Latest Activity

Ed Minch commented on Tom White's video
Thumbnail

Measured Home Performance: Assessment with a Infrared Camera

"I find it best to scan one time before the Blower Door is used to check for insulation and…"
7 hours ago
Profile IconLarry Kinney and teplie_poly joined Home Energy Pros
11 hours ago
Dan Antonioli replied to Dan Antonioli's discussion Net Zero Energy Hot Water
"Okay, a couple of things. The 1.0 kW per square meter reference is only under the most ideal lab…"
22 hours ago
Hans Joachim Preiss replied to Dan Antonioli's discussion Net Zero Energy Hot Water
"Dan, Let me attempt to compare apples with apples: My solar thermal system is located in…"
23 hours ago
Dan Antonioli replied to Dan Antonioli's discussion Net Zero Energy Hot Water
"Hi Hans, I don't know where you're located but where I am a 2.5 kw pv system costs closer…"
yesterday
Hans Joachim Preiss replied to Dan Antonioli's discussion Net Zero Energy Hot Water
"I use the combination of solar PV and heatpump water heaters in the vast majority of net-zero…"
yesterday
Amber Vignieri posted a blog post
yesterday
William Zwack added a discussion to the group Job Board
Thumbnail

Residental Energy Specialist: Washington, DC (or possibly telework)

Position Summary: CSRA Incorporated is searching for a Sr. Residential Building Energy Efficiency…See More
yesterday

© 2016   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service