Heating and cooling load calculation
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  1. #1

    Heating and cooling load calculation

    Hello everyone,

    I'm a senior in college trying to finish up my senior paper, but I'm stuck on calculating the heating and cooling load of a single family residence. Basically, I am comparing a normal home (natural gas furnace and split system central air) to one with passive solar considerations and a geothermal heat pump. I have used some free online programs and tried to calculated it myself, but the numbers never seem right.

    So my question is really are there any free resources to calculate heating and cooling load? And also, what should i expect the heating and cooling load of a 2,400 square foot in New Jersey to be?

    Thanks in advance.

  2. #2
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    Moved to General Discussion forum.
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  3. #3
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    Perhaps you should post your results from the loads you did.
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  4. #4
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    Thumbs up ACCA MANUAL J obviously needed

    Quote Originally Posted by Saul Goodamn View Post
    Hello everyone,

    I'm a senior in college trying to finish up my senior paper, but I'm stuck on calculating the heating and cooling load of a single family residence.
    free online programs and tried to calculated it myself, but the numbers never seem right.

    , what should i expect the heating and cooling load of a 2,400 square foot in New Jersey to be?
    .
    www loadcalc net
    Quite Good + Simple .

    Analysis accuracy is just about the same as situation one finds for equipment functionality and the resultant comfort ...
    it all depends on the Installer.

    There is no 'typical' house because it could be a very leaky, non-insulated 120 year old building or
    a new designed residence with foamed sealed roof deck, ducts in conditioned space and with VERY Good Windows.

    Amount of windows could be 200 or 400 square feet, single, double or insulated glass.
    Infiltration (ACH) could be 0.15 (tight) or loose (0.8)

    Having said that, ...
    MY Typical recently built 2,400 Sq Ft good construction Mid-Atlantic Home might be something like-

    Cooling 25,000 BTU/HR +/- 12%
    Heating 40,000 BTU/HR +/- 12%

    ,,, less with ducts in conditioned space and tight construction
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Quote Originally Posted by dan sw fl View Post
    www loadcalc net
    Quite Good + Simple .

    Analysis accuracy is just about the same as situation one finds for equipment functionality and the resultant comfort ...
    it all depends on the Installer.

    There is no 'typical' house because it could be a very leaky, non-insulated 120 year old building or
    a new designed residence with foamed sealed roof deck, ducts in conditioned space and with VERY Good Windows.

    Amount of windows could be 200 or 400 square feet, single, double or insulated glass.
    Infiltration (ACH) could be 0.15 (tight) or loose (0.8)

    Having said that, ...
    MY Typical recently built 2,400 Sq Ft good construction Mid-Atlantic Home might be something like-

    Cooling 25,000 BTU/HR +/- 12%
    Heating 40,000 BTU/HR +/- 12%

    ,,, less with ducts in conditioned space and tight construction
    I have actually been pretty much exactly the numbers you are suggesting. They just seemed to be too low.

    Cooling: 25,000 btu/hr
    Heating:42,000 btu/hr

    So does this mean I would need a 50,000 btu/hr furnace (assuming 80% efficiency) and a 2-ton AC?

  6. #6
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    25,000 BTUH heat gain will not be served properly by a 2 ton (24,000 BTUH) A/C, you'll be short 1,000 BTU an hour, assuming you even get the full rating of the listed tonnage. You can go up 25% of your load calc without being concerned about losing control of the humidity SO 25,000 *1.25 = 31,250 BTUH, so a 2.5 ton will meet your 25,000 BTUH load without exceeding the 31,250 BTUH max.

    Same story with your heating, except you can go higher than 25% over without problems. Never go under your load calc. Not sure what your next size is but I assume 75k BTUH. @ 80%, that would be 60k output.

  7. #7
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    And as Dan stated, you need to use Manual J. Your numbers might be low, they might even be high. Manual J will tell you.

    Basic single story 2400 sq ft house built with construction materials you can pick out (since you're just spec'ing it for a paper), you should be able to do in 10 minutes.

  8. #8
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    Try Hot2000 - simulates energy performance but also calculates load.

    Not a professional opinion:

    I can see a new, tight 2400 sq ft house built with r-20 walls only needing 42 000 btu/hr of heat, but 25k btu of cooling seems a little low unless it's facing north-south and has lots of shading. I would guess 2.5-3 tons.

  9. #9
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    Manual J has some fudge factors built in. Not cool enough complaints are rarely caused by undersizing the system. Most not cool complaints are related to poor installation, bad ductwork, or poor thermal envolope. If you cut sizing close it MUST be installed RIGHT, no room for poor installation practices. A typical system only delivers about 65% of it's rated capacity, 65% real world capacity won't cut it if the system is sized correctly.

    My own 1600sqft 14yr old house has a 2 ton unit and will keep it 75f inside on a 100 degree day. If the 2400sqft house you are building is tight 2 tons may be enough that far north. Ductwork will most likely need to be in conditioned space for 1200sqft per ton to be effective. If you are undersized the thermal mass of the house will limit the amount the system misses setpoint during times when design conditions are exceeded. If you can live with 78f instead of 75f for a few afternoons in the summer then undersizing does no harm. You will more even tempatures and lower utlity bills the other 95% of the time.

    http://acrightsize.com/files/elephant_in_the_room.pdf

  10. #10
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    I'm here in south central Arizona. I just did a manual J using a couple of different programs and they are saying that my house has a heat gain of around 19k-20k BTUPH.
    I have a Goodman 4-ton heat pump w/TXV and I am very happy with it.
    Looking at Goodman's 'expanded cooling data', I could have put in a much smaller unit, but I wonder if the 'manual' considers things like extended periods of time when the OAT's do not drop below 100* during the summer, day or night.
    Over time the insulation of a home will absorb all that heat and fail to keep a proper barrier between the conditioned space.
    So, my question is the 'manual' reliable under these extreme conditions?

  11. #11
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    Quote Originally Posted by timberlinemd View Post
    I have a Goodman 4-ton heat pump w/TXV and I am ...

    So, my question is ... ?
    ... Are you a frequent hijacker?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  12. #12
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    Quote Originally Posted by timberlinemd View Post
    I'm here in south central Arizona. I just did a manual J using a couple of different programs and they are saying that my house has a heat gain of around 19k-20k BTUPH.
    I have a Goodman 4-ton heat pump w/TXV and I am very happy with it.
    Looking at Goodman's 'expanded cooling data', I could have put in a much smaller unit, but I wonder if the 'manual' considers things like extended periods of time when the OAT's do not drop below 100* during the summer, day or night.
    Over time the insulation of a home will absorb all that heat and fail to keep a proper barrier between the conditioned space.
    So, my question is the 'manual' reliable under these extreme conditions?
    Yes, its reliable. So you have an oversized system, that cost more to use.
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  13. #13
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    Quote Originally Posted by dan sw fl View Post
    ... Are you a frequent hijacker?
    Not 'frequent'

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