Geothermal Loads - Cooling or Heating Factors
Last Post 03 Nov 2007 01:02 AM by tuffluckdriller. 4 Replies.
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trmontgomeryUser is Offline
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31 Aug 2007 01:30 PM

This is our first summer in our newly built stick home.  We have been experiencing our home warming as much as 8 degrees (almost 80 degrees in the house) during warmer days when the sun is out.  We live in Iowa and our home does face the South with many huge windows.  We even tinted the upstairs windows in hopes this would help reflect some of the UV heat.  Our heating and cooling company ran loads on the house based on the direction the house sat, color of roof (black), and window area, and ceiling height, but chose to select our needs based on the heat load primarly.  We even told them we would not be putting window coverings over the windows prior to building our home!  The tech has been out and stated everything is running properly.  The owner of the company told us to put window coverings up (there goes the views!) and provided no other solutions.  The system pretty much runs non stop during the summer.  Any ideas?  Should the company have run the loads based on cooling needs or heating needs primarily? Even the basement is warm.  We have a 5 ton system to heat/cool 4800 sq feet and another 3 ton system to provide domestic hot water and run the radiant in the basement.  Help! 

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31 Aug 2007 03:42 PM
Posted By trmontgomery on 08/31/2007 1:30 PM

This is our first summer in our newly built stick home.

That was your 1st mistake.

We have been experiencing our home warming as much as 8 degrees (almost 80 degrees in the house) during warmer days when the sun is out.  We live in Iowa and our home does face the South with many huge windows.  We even tinted the upstairs windows in hopes this would help reflect some of the UV heat.  Our heating and cooling company ran loads on the house based on the direction the house sat, color of roof (black), and window area, and ceiling height, but chose to select our needs based on the heat load primarly.  We even told them we would not be putting window coverings over the windows prior to building our home!  The tech has been out and stated everything is running properly.  The owner of the company told us to put window coverings up (there goes the views!) and provided no other solutions.  The system pretty much runs non stop during the summer.  Any ideas?
I would add film to the rest of the South facing windows. Llumar and VISTA are 2 films that I know of. You should get a 50% to 75% reduction in heat gain. I used a similar film on sliding glass doors in Omaha, and the results were great. But remember, you are not trying to tint the windows, you are trying to reflect the heat!

Should the company have run the loads based on cooling needs or heating needs primarily?
You will find that many companies just use a standard gain/loss figure and don't perform heat loss/gain calculations for each house. And, if you have a well insulated house, your heating and cooling equipment can be oversized. And oversized equipment can present it's own set of problems.

Good Luck!
....jc<br>If you're not building with OSB SIPS(or ICF's), why are you building?
dmaceldUser is Offline
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17 Sep 2007 11:59 PM
Posted By trmontgomery on 08/31/2007 1:30 PM

We even tinted the upstairs windows in hopes this would help reflect some of the UV heat.


Did you tint them, as in just putting some sort of color on them, or did you put a reflective coating on them? If you only tinted them, you may have worsened the situation. My boss had a west window tinted in a print shop I worked in years ago. All it did was absorb the sunlight, converted it into heat, and transformed the window into one huge radiator! With drapes closed the air between the drape and window exceeded 120F.


Ask the HVAC contractor to go over the heating/cooling load calculations with you. If it shows your cooling load to be greater than your heating load, and he sized the equipment properly for the heating load, you have your basic answer right there. If by chance he sized it for heating only by the "by guess and by gosh" approach, he has a problem.

I take it the 3 ton unit is a heat pump. If so, ask your contractor about using it to supply a cold water coil installed in the supply ducting to provide more cooling.


Even a retired engineer can build a house successfully w/ GBT help!
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18 Sep 2007 12:51 PM
I don't think anyone needs to run any calcs to figure out that your system is undersized. The results speak for themselves. It's difficult to believe that an HVAC contractor would seriously think that each ton of AC in Iowa could handle nearly 1000 square feet of conventional stick built home with large south facing windows.  It is surprising that your home only gets to 80 inside. It must have been insulated pretty well.

If the HVAC contractor designed the system it is his responsibility to fix it. Only a larger unit will do that. Could get very expensive.

BTW, if he designed an extra 3 ton of supplemental heat he actually might have calculated for both cooling and heating - he just made an error along the way -  or maybe used a standard rule of thumb for the ratio of heating to cooling for your area. Sure hope you have enough heat for the winter.
tuffluckdrillerUser is Offline
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03 Nov 2007 01:02 AM
The biggest mistake it seems they made is that they sized for heating, when the cooling load may have been the larger load. A proper load calculation will always take heating and cooling into consideration. The idea is to not oversize one or the other too much to meet the higher load.

When cooling is the higher load, the ground loop considerations become very important. MUCH design considerations need to be addressed to decide if there will be enough loop. As geodean says, if the loop water temperature gets too hot, there cannot be much cooling performed by the heat pump. When the loop gets too hot, it's a big sign that the loop is either under sized, or the system is undersized. You definitely can't just guess that the heat pumps are too small.

You need to have someone qualified look at doing a load calculation as acurately as possible, and look at the complete design of the ground loop.
Clark Timothy ([email protected])<br>Geothermal Heat Pumps: Heating and Cooling that's Dirt Cheap!<br>www.pinksgeothermal.com
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