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  1. #1
    Join Date
    Mar 2016
    Location
    Dayton Oh
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    Load calc cant be right.

    Looking for a second brain I dont trust my software. Technically I need manual N, but my software is only J so its what im using.

    The building:
    Old building from the early 1900, used to be library but is now a converted office. Im working on the basement/lower level unit. There are 2 units for the level im calculating 1 of them. Construction is triple brick then a empty metal stud space then drywall. I used R2 for my exterior walls. Windows are single pane but have a good sealed storm on them, so double pane clear glass. Walls are 9' tall but 2' of that is below grade. Only south and west walls have exterior exposure. Above is finished conditioned so no lose to rooms upstairs, other half of floor is conditioned so no loss there. The load is coming from the floor, two exterior walls, and people. no major appliances other than computers (like laptops and desktops). No exterior doors, those are done with the other system.

    I came up with finished numbers of 24155 heat, 16067 cool w/ 4130 of that being latent.

    50' south wall w/ 120 sqft window. 350 sqft above grade 100 sqft below grade.
    26' west wall w 45 sqft window. 182 above grade 52 below grade
    floor 1300 sqft
    cubic ft 11700
    below average construction.
    ducts conditioned
    people 10

    I believe there is a 4 ton and 100k furnace. I believe, when these units were put in 18-20 years ago it was part of a big project, so i would assume the units were engineered (sizing and duct work). Ductwork is done really well, and the two units upstairs have superbly laid out and installed duct work as well. So the original install wa snot hacked in to say the least. But the sizing of what is there now and what my numbers say is very very different.

    Wanting someone who has more experience in this to chime in.

    (Rereading my post, and looking at my numbers, and walking throught the building in my head, I feel they are starting to make more sense....)

  2. #2
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    44,190
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    All I can do is guess, based on what I see down here in Atlanta...

    BOTH numbers look light...

    Sometimes, I go to a weeknight trivia at a Tavern... building is from pre-civil war, with multi/layer brick walls and a beam roof... restaurant has multiple package units on the ground, with spiral ducting at the ceiling.
    Not sure if that helps any...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *Cheap is not good, good is not cheap; however expensive is not a guarantee of quality!
    Choose your contractor wisely!

  3. #3
    Join Date
    Mar 2016
    Location
    Dayton Oh
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    Thread Starter
    Your climate might be a tad bit different than mine. Not much just a little.

    I have been chewing this on and off all day. The old adage was 400 sqft/ton which would work for a house from the 50 no insulation and 4 exposed walls.

    I’m at 650 sqft/ton and only 2 walls. Idk.

    Where is Larry K or danswfl?


    Sent from my iPhone using Tapatalk

  4. #4
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    44,190
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    For a resi... we usually assume the standard family of Mom, Dad, 2x kids... and there is cooking, clothes, hot water, etc...
    Residential = more MUA and more heat sources...
    Library = more MUA (breathing and air changes)... almost no heat sources.
    The library would be more warm bodies... last I remember 3-4 warm bodies = a ton of AC.

    Might consider 2 stage... give yourself some margin to handle swing season as well as peak loads...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *Cheap is not good, good is not cheap; however expensive is not a guarantee of quality!
    Choose your contractor wisely!

  5. #5
    Join Date
    Aug 2013
    Location
    Visalia California 93291
    Posts
    7,721
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    I would take a 1C window SHGC and U are still pretty close......ducts in conditioned space and no roof load I'd say you are closewitjout looking @ it

    you really don't need N on this from what I see ,but you can download N from Elite and use the free trial

  6. #6
    Join Date
    Jan 2015
    Location
    San Diego, CA
    Posts
    428
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    Your results could well be correct - I have been surprised at the results I've got for some of my customers but when I thought it through and looked at everything it made sense.

    Did you add any appropriate internal loads - such as lights, refrigerator etc.

    What software are you using?

  7. #7
    Join Date
    Oct 2011
    Location
    Culver, Oregon (Central OR)
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    Oversize the units and ducting with variable capacity equipment and have dampers installed throughout the duct system?

  8. #8
    Join Date
    Mar 2016
    Location
    Dayton Oh
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    Thread Starter
    Im going to go with it. Times I have doubted the end result but they ended up being correct. I swung by today to see what was in there cause I forget, they have a 5 ton and a 120k. So when I see 18k cool and 24 heat i get worried. Like I said before around 20 years ago when the building got converted from an old library with steam heat to offices with forced air and steam, I would have assumed it would have had an engineer size the units. which made me question my numbers again.

  9. #9
    Join Date
    Mar 2016
    Location
    Dayton Oh
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    Thread Starter
    They wont spend the money on variable. not a chance. I will say, ducts are actually sized for 5 tons. Dampers are already installed in all branches.
    Added in the 10 people, and 10 computers, all lights are LED but yes did add them in. No other loads come to mind. No fridge or stove, no coffee maker, no copy machine. Literally 10 people sitting on their computers talking on the phone.

    This all started because they are/did turn a conference room into offices, and I had to add the ducts. In order to get an airflow number you need the load, so I told them at end of project I would release the block and room by room load as part of my job for them to have in the future. Got my numbers and CFM needs, and just started saying cant be. But the more I think on it the more I believe it. Its really not that big of a space @ 1300 sqft but mentally i just struggled with the current equipment.

    Handed him the loads today, he asked what was in there now, and I told him. He said they seam to be working fine and the women prefer it be warm in the building, I said good.

  10. #10
    Join Date
    Jan 2015
    Location
    San Diego, CA
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    428
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    In my area a lot of older systems are oversized - most likely installed based on the old addage. I have seen similar numbers to you on homes even bigger but there had been improvements to the home which helped bring the numbers down such as the installation of low-e glass etc.

  11. #11
    Join Date
    Oct 2011
    Location
    Culver, Oregon (Central OR)
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    So you are going with smaller equipment?

  12. #12
    Join Date
    Mar 2016
    Location
    Dayton Oh
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    Thread Starter
    Quote Originally Posted by Adlerberts-Protege View Post
    So you are going with smaller equipment?
    Not at this time. Everything is working I was there to add Supply and return to the newly converted space. When they fail I’ll install smaller. If I get the job.....


    Sent from my iPhone using Tapatalk

  13. #13
    Join Date
    Oct 2011
    Location
    Culver, Oregon (Central OR)
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    Quote Originally Posted by jbhenergy View Post
    Not at this time. Everything is working I was there to add Supply and return to the newly converted space. When they fail I’ll install smaller. If I get the job.....


    Sent from my iPhone using Tapatalk
    Be interesting to see if it's short cycling. May be time to invest in a good data-logger?

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