Results 1 to 8 of 8
  1. #1
    Join Date
    Aug 2010
    Location
    North East Iowa
    Posts
    21

    HVAC design for super tight, efficient house

    I design buildings to be efficient, but I have really no idea on HVAC items to match them. I believe putting the money into your shell first, then hvac to fit the needs.
    Here is some back ground: new construction, Single story house w/ walkout basement (facing north) in NE Iowa. Upper conditioned space is about 1550, plus a bonus room over the garage that is about 400 sqft. I would be fine if this was a stand alone system as well, as we will probably only use it for storage at first, finishing it out completely later.
    Basement has family area, 2 bedrooms, bathroom and 2 storage rooms. True conditioned space is about 1250.

    Construction type is staggered 2x4 studs on 2x8 plates with blown cellulose fill, then 1.5" XPS exterior insulation with drainage plane. ALl plates caulked to floor and to each other, XPS caulked to stud face, spray foam around electrical penetrations, etc. Basically as sealed as possible. R-60 cellulose in the attic.

    Openings are high performance fiberglass with U around .27. South windows (not that many) have u .35 with SHGC of around .5.

    After some very generic load calcs, it looks like a 2 ton 2 stage system is the most we need, even pushing the high side. I am attempting to figure out the cost of operating different systems.

    We do not have NG at the location, so it would have to be propane. However I would prefer to do an all electric option. The rates around here would be about .1, however with the all electric plan, they drop during the winter months to .04 after the first 600kw are used. THen for summer usage, they jump to .18 after the first 600 is used. However this applies to 3 or 4 months out of the year, I believe the rest are the .04 months.

    here are my thoughts: The demand for heat with this house will be low enough that geo probably will not pay for itself in 15 years or less, which is the guested time we will live there. SO I have been looking into air handlers with electric strips and air to air HP options.

    Here are some numbers: Waterfurnace 2 ton 2 stage geo, horizontal loops, HRV, electric strip, all duct work- $$$$- fed credit= $$$

    more "standard option"-
    Lennox CBX27UH-024 blower coil w/ electric heat strip
    XP16-024 2 ton 16.5 SEER HP.
    HRV, auto switch over thermostat, all ducting and load calcs- $$

    adds would be 2 ton 19 SERR HP- $
    CBX32MV-024 blower coil- $
    CBX40HV-024 Blower Coil- $

    so basically just over a $$ difference. I am trying to get operating cost estimates from them as well.

    any thoughts on the situation?

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,364
    I have a similar house in WI. I have had a heat pump and switched to conventional a/c and LP. I have added a ventilaing dehumidifier to maintain <50%RH throughout the spring/summer/winter because of low cooling load on the home and the developed basement. The home needs some ventilating in the winter when the wind is calm and the temps are +20^F. During cold windy, no supplemental ventilation needed. During the rest of the year, need fresh air ventilation. I use CO2 to activate the fresh make-up air ventilation. I suggest using CO2 control to minimize the ventilation only when needed.
    If you are sure that you will need enough fresh air ventilation to get payback from an air exchanger, I suggest you consider an ERV instead of the HRV. It will help with summer moisture and may help save moisture during cold dry winter ventilation. I assume "no open combustion like wood burner or fireplace". Unless you have +4 occupants, you will need humidification during <10^F outdoor dew points with an air change every 5-6 hours.
    I my case, by minimizing the ventilation operation to time of occupancy and low winds, An erv has minimal payback. Because of the developed basement and fresh air ventilation, maintaining <50%RH is important to avoid an inivitable musty basement. These well insulated home do get enough a/c run time to remove the upto 5 gals. per moisture load from fresh air and occupants.
    I like your recognition of the need for fresh air a well built home. Keep us posted.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  3. #3
    Join Date
    Aug 2010
    Location
    North East Iowa
    Posts
    21
    what were your reasons for switching from a HP? I am guessing your backup was too expensive for the climate? However I would think propane would be pretty pricey as well?
    Propane would be my gas option in our area.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,364
    Quote Originally Posted by lzerarc View Post
    what were your reasons for switching from a HP? I am guessing your backup was too expensive for the climate? However I would think propane would be pretty pricey as well?
    Propane would be my gas option in our area.
    LP cost <$1200 per year to heat, payback on GShP would be for ever. Maybe at your rates HP would work out better?
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
    Join Date
    Oct 2010
    Location
    Athens, OH
    Posts
    13
    Not completely related but Izerac, R60 in attic-nice, does that demand you use 5/8 drywall on the ceiling? I'm puttin in R38 and am thinking of using 1/2" at 24 inch oc spacing...

  6. #6
    Join Date
    Aug 2010
    Location
    North East Iowa
    Posts
    21
    I believe code requires 5/8" on the attic. If not, definately do 5/8" regardless. Even an r-28 could have a sag or possibly screw pops.

  7. #7
    Join Date
    Aug 2010
    Location
    North East Iowa
    Posts
    21
    my local utility company who has a very large focus on energy efficiency and has several great programs sent me this very detailed spread sheet. basically I can input the equiptment SEER numbers, COP, efficency, etc as well as electric rates and gas rates. It then calculates, based on a 10 year average HDD factor, annual cost of an air source HP w/ electric backup, ground sourse HP w/ electric backup, air source w/ natural gas backup, and finally natural gas only.

    If I assume 30k BTU requirement, which I think is inline for this house, and a 5,291 HDD....
    using a 16.5 SEER HP at 24,000 btu vs a geo HP with 4.0 COP and 21,000 BTU, its telling me my annual heating cost is $450 for the air HP and $302 for the geo. This is based on a .07 electric cost average (since it adjusts after 600 Kw). Both are 200+ less then gas.
    Does this sound right? If this were the case, we are looking at 20 years for a geo payoff, including tax credit. (at only a $150/year savings)

  8. #8
    Join Date
    Mar 2007
    Location
    Orange County NY
    Posts
    212
    Quote Originally Posted by lzerarc View Post
    I design buildings to be efficient, but I have really no idea on HVAC items to match them. I believe putting the money into your shell first, then hvac to fit the needs.
    Here is some back ground: new construction, Single story house w/ walkout basement (facing north) in NE Iowa. Upper conditioned space is about 1550, plus a bonus room over the garage that is about 400 sqft. I would be fine if this was a stand alone system as well, as we will probably only use it for storage at first, finishing it out completely later.
    Basement has family area, 2 bedrooms, bathroom and 2 storage rooms. True conditioned space is about 1250.

    Construction type is staggered 2x4 studs on 2x8 plates with blown cellulose fill, then 1.5" XPS exterior insulation with drainage plane. ALl plates caulked to floor and to each other, XPS caulked to stud face, spray foam around electrical penetrations, etc. Basically as sealed as possible. R-60 cellulose in the attic.

    Openings are high performance fiberglass with U around .27. South windows (not that many) have u .35 with SHGC of around .5.

    After some very generic load calcs, it looks like a 2 ton 2 stage system is the most we need, even pushing the high side. I am attempting to figure out the cost of operating different systems.

    We do not have NG at the location, so it would have to be propane. However I would prefer to do an all electric option. The rates around here would be about .1, however with the all electric plan, they drop during the winter months to .04 after the first 600kw are used. THen for summer usage, they jump to .18 after the first 600 is used. However this applies to 3 or 4 months out of the year, I believe the rest are the .04 months.

    here are my thoughts: The demand for heat with this house will be low enough that geo probably will not pay for itself in 15 years or less, which is the guested time we will live there. SO I have been looking into air handlers with electric strips and air to air HP options.

    Here are some numbers: Waterfurnace 2 ton 2 stage geo, horizontal loops, HRV, electric strip, all duct work- $$$$- fed credit= $$$

    more "standard option"-
    Lennox CBX27UH-024 blower coil w/ electric heat strip
    XP16-024 2 ton 16.5 SEER HP.
    HRV, auto switch over thermostat, all ducting and load calcs- $$

    adds would be 2 ton 19 SERR HP- $
    CBX32MV-024 blower coil- $
    CBX40HV-024 Blower Coil- $

    so basically just over a $$ difference. I am trying to get operating cost estimates from them as well.

    any thoughts on the situation?
    Do a search for heatcalc.xls 1.09 for operating costs, and look at Daikin Altherma.

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