Sizing and Heat Loss Calcs

Discussion in 'General Discussions' started by mseifert, Aug 31, 2009.

  1. mseifert

    mseifert Member

    I am in the process of getting quotes for adding a horizontal ground loop, water to water geothermal heating system (no A/C) to my existing propane heated hydronic system (I would retain the propane as auxillary heat). I am in Idaho where the nearest cities are 75 - 90 miles away. The local town expert (everyone has referred me back to him and references are good) has not offered to do a heat calc. The guys from the the cities aren't offering to come out any time soon to do one.

    So I have used 3 online heat loss calculators to do my own (I acted as "general contractor" in building the house so I have the specs). The 3 programs are at: ... atLoss.htm

    All three show from 54k - 58k btu/hr design heat loss. My house is a 3500 sq ft stick frame house with straw bale infill. The rest is blown-in cellulose (roof, floor, & walls that don't have straw). I'm using a design temperature of 0 degrees F.

    For the 18" straw walls which also have 3 1/2" fiberglass in the framing, I'm choosing r40. I'm assuming r3.5 per inch of cellulose.

    The local guy has quoted $15,800 for the ClimateMaster Tranquility TMW 060 (5 ton) - excavation not included. The unit is rated at 51,000 btuh (at 104 / 32 degrees).

    My Questions: Is the ClimateMaster unit big enough to handle it? Are the heat loss calculators reasonably accurate? And is $15,800 a fair price? I'm getting a second quote for the identical system from another dealer.

    One of the city dealers said he would recommend a Hydron Module 6 ton unit. Someone else on this site mentioned the Hydron Module Combination unit as a way of getting Energy Star rating now and still doing Water to Water. Is this a good idea? Is Hydron Module on par with ClimateMaster?

    Thanks for your feedback. There isn't a lot of unbiased local advice I can get.
  2. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    5 ton sounds reasonable, you will need some sort of auxiliary heat.
    Nor is there anything wrong with Hydron.
    The radiation is the key here, hopefully you have a good pipe network as geo can only get the water so hot in January.
    Price sounds cheap. I know you said excavation not included, are they still doing the loops?
    I'm not a fan of contractor's who don't take the time to do their heat loss calcs. I will tell you though, when I measure for load, I'll guess the unit size and then support it with calculations. I don't remember the last time I guessed wrong. Some contractors take this a step further and guess without backing it up with calcs.
    Climate master doesn't have every tonnage available in water to water, so if selecting between a 3, a 5 or a 10 ton unit, most folks would gravitate toward the 5.
    I think you will find water to water will be tax credit eligible eventually, but you will have to meet efficiency requirements.
  3. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Getting an installation done off your own calc's might be a bit risky. Fine to get quotes that way. But make sure your installers do their own designs (our source them) so they remain accountable.

    Someone still has to size the heat pump to the heat loss. As much as we try to simplify things by saying this unit puts out X Btu's and can match this heat loss/gain, it is a bit more complex (EWT's, % design load, bin load hours, and so forth).

    You stated a design temp - just ensure that is the recommended design temp. for your area as well.

    Both units you've mentioned are good suppliers.

    So to sum up, you look like you're on the right track. Just make sure you don't take the onus off the installer to do their job. Using these numbers for quotes is fine, but be prepared to see a design (likely after making a deposit$) before your system is finalized.
  4. GeoXNE

    GeoXNE Guest


    Please keep in mind with a water to water system the load side hydronic design is just as important as the incoming source design.

    The heat emitters (radiant floor, fan coil, baseboard, radiators, etc.) must be designed to supply the needed BTUs at temperatures well below the typical fossil fuel boiler and within the operating parameters of the heatpump. Improper load temps and flow can lockout a w-w heatpump just as fast as an improperly designed source loop field.

    Also if you use your existing boiler for aux the w-w unit must be protected from the higher temperatures.
  5. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I agree that the load calc should be entered into design software by your pro's. It is possible that the 3 ton unit will satisfy most of your heat load for a much lower install cost.
    What major city are you closest too?
  6. mseifert

    mseifert Member

    Thank you for the encouragement. Once I am ready to put down a deposit, I will ask for this. Accountability was the key word.

    Where I live there is no temperature data. I am basing it on my experience. -10F happens maybe 5 evenings a year (-10F adds 8,000 BTU extra in the calculator). -20F is a rare evening occurrence. So design of 0F should handle the load 90+% of the time.

    Thank you for the warning. My hydronics propane heater (Quietside QVM9) can go as low as 104F. What is the max temp for a Geo System? The flow is another thing. I'll make sure the installer covers all the bases with this.

    Spokane, Washington

    Thanks everyone for your input.
  7. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Taking advantage of the lower temps, all about flow through the system and the design of the heat emitters and their supply system.
  8. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    According to my (Elitesoft) software Spokane, WA calls for a design temp of 2 Deg F as a 99% value.

    Unless you are in a micro-climate substantially cooler than Spokane design temps then Joe Ami's suggestion of a substantially reduced tonnage unit should be carefully considered.

    Dropping the tonnage dramatically cuts installed cost and increases summer cooling comfort with better dehumidification at the minor expense of having to run supplemental strip or other heating a few hours during the coldest nights each year.
  9. mseifert

    mseifert Member

    Where I am is colder than Spokane by 10-15F. Does your program have data for Sandpoint, Idaho? I'm colder than Sandpoint by 10F, but since Sandpoint is within 15 miles of my home, I can gauge this more accurately.

    Thank you for stressing I need to do my homework here. Hopefully between the geo system installer and the radiant floor designer, I can get the info you are referring to. Is there anything I can do as a homeowner to figure this out? What questions would I need to ask besides gpm?
  10. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    You mention existing Hydronic systems

    What is there and what is the entering water temperature to the system? What type of heat emitters are you using?

    The issue is how low a temperature can you feed your emitters. A radiant floor or panel will run and keep you comfortable, (with properly spaced tubing) using EWT of 80* or maybe less. The spacing and r-value of the floor covering dictates the BTU per square foot out-put. Using 3/4" copper fin-tube we need 180* water to produce 600 BTUH/linear foot. The fin-tube will work at lower temps, (I can not find my chart), but we may not have enough linear feet of wall to cover the design day heat loss.
  11. mseifert

    mseifert Member

    Our hydronics are 1/2" pex tubing spaced 8" apart.

    On the main floor the pex is embedded in a 3 1/2" slab over a framed floor. The framed floor (under the hydronics) is 2x8 construction with blown in cellulose (approx r26). The space below the floor is a 3' vented crawl space with the vents blocked during the winter months. The hydronics are a closed loop system heated by a Quietside QVM9 (propane & no storage tank). On top of the slab throughout the house is either Travertine tile, softwood floor or carpet in the bedrooms.

    On the 2nd floor, it is also embedded in a 3 1/2" slab - but this slab sits on the first floor ceiling.
  12. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Only thin my software had reasonably proximate was Lethbridge, Alberta CN, but that's way North of you. The deeper we get into the question, the more I'm convinced that you need a local pro on the hook for sizing.
    You need to know actual temp that your radiant is designed for and actual man. J load calculated from a real 20 year weather average, not numbers from a hat.
  13. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I spent a bit of time with my s/w weather database trying to home in on your situation. I'm skeptical that you are 10 degrees cooler than a town 10-20 miles away unless you are at a substantially higher elevation than that town - though that's perfectly possible in mountainous terrain.

    It is awfully tempting but must be avoided to think "well, it got down to minus umpteen degrees one night 3 years ago so we'd better size the heat pump for that" Record cold days are few and far between and heat strips, (and sweaters) are an effective alternative to those conditions.

    Joe is right - you need 'boots on the ground' local expertise rather than we internetters making wild guesses.
  14. mseifert

    mseifert Member

    It's like that in the mountains where I am. Down in the valley is beautiful Lake Pond Oreille which due to its mass buffers the surrounding area. I am also 500 feet higher in elevation and added to losing the "lake effect", puts me in another zone.

    No worry, the ClimateMaster dealer agreed to doing a heat calc once I sign a contract. He said the design temperature here is -5F (Sandpoint is +5F).

    Interestingly, he said his rule of thumb is 17 btu/hr per sq ft for a well insulated house. Using this, he comes within 300 btu of my programs. After the hours of inputting data to get my numbers, his "rule of thumb" sure surprised me to come within 1/2%. Granted it is not a "professional program" like everyone is asking for, but I'll bet it won't be much different when we're done.
  15. Bergy

    Bergy Member Industry Professional Forum Leader

    The heat gain/heat loss calculations MUST be done before you sign a contract!! The unit is sized according to those numbers so you might sign a contract for a unit bigger than you need.


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