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Manual J

Starch
Starch Member Posts: 102
in THE MAIN WALL
....where can I get information on this cooling load calc. method you refer to? I've never heard of that one before.

Starch

Comments

  • TBK1
    TBK1 Member Posts: 14
    Manual J

    just got done studying the manual J calc for heat gain and loss, then got told if u use it u will be sorry in the cooling area, did A book calc on a 2200 sgft and came up 1.5 ton cooling req. Whats the veiws here, do we trust it or back to the standard of 600 per ton!
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    I do Hydronics only now, but

    I took a mechanical engineering class and then went to work for my instructor's engineering firm (thier specialty was hospitals in Chicago) and the calculation method we used then was the Cooling Load Temperature Difference (CLTD)method. I've used it on my own home, a 2800 sq ft 1906 frame home with large glass area, some shading on the south, and well insulated and end up with a 28,000 btu/hr load for northern Illinois. We are currently using 1.5 tons of window units and can keep the home at 75F average temp in the worst of weather. My mother's old brick home in Chicago, about 2,000 sq.ft. with lots of shade west and south, had two very old one ton window units and you could make the house a freezer in extreme heat. Did a cooling calc for my former church, an 1850 stone sturcture that seats about 200 people with a 20 foot heavily insulated ceiling and it only needed 6 tons cooling. That's what was installed and it works. Things like building mass and shading have a huge impact on cooling loads. I believe cooling equipment oversizing is just like that in heating equipment...a national pastime. Oversizing cooling equipment can leave you with cool damp air, and, that dreaded mold problem.


    Boilerpro
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    Not sure right now, but

    It was the accepted practice back in the mid 80's, I believe. I have it in my old textbook from the class. "Mechanical and Electrical Equipment for Buildings", 7th Edition, By Benjamin Stein, John S. Reynolds, and William Mc Guinness. Published by John Wiley and Sons, Copyright 1986. It was orignally from the ASHRAE Handbook of Fundamentals, 1981. Nice load calculation. Takes into account solar position, building mass, furnishings mass, length of occupancy, interior shading, exterior shading, and some other variables. Hope this helps.


    Boilerpro
  • Caselli
    Caselli Member Posts: 40
    I ALMOST have that book

    I thought, "Yes. I have that."
    Nope. I have the Fifth Edition, 1971.
    Great book. If you want to learn about psychrometric charts, this is a great place to start....
  • Anthony Mobilio_3
    Anthony Mobilio_3 Member Posts: 62


    I learned the manual method and went out and purchased the right j software. Have been using it for 10 years. Never had any trouble in sizing for heating or cooling. Just make sure all your inputs are correct glazing areas and direction of windows, R values and design temp are correct. Do you have the Manual J book, where did you learn how to do the calculation.

    Anthony
  • TBK1
    TBK1 Member Posts: 14


    yes i have the new manual j, think its seventh or eigth edition, was taking course in pchyclometrics , duct sizing, air properties and is being taught in their, at a tech college
  • TBK1
    TBK1 Member Posts: 14


    it appears that the design temps of certain areas that the book tells u to use are way out of norm.
    an example is in the south here, it tells u to use 90 as an average high and 25 as a low. hell it aint even summer here yet and we are in the mid nightys most the time, and winters will def drop below 20's . and yes i know i could just use my own temp ranges but doesnt that defeat the book being the "STANDARD"
  • Anthony Mobilio_3
    Anthony Mobilio_3 Member Posts: 62


    I don't have my book in front of me. On the software you can choose the bin weather data for your area. It should be in the book also. It shows how may times and at what temp.it got for your general area. That will determine the design temp for that areas. In Connecticut we use 0* heating 95* cooling. Do you have the weather data in that book. Looking at CT data for cooling it was 95*-100* for 3 hr. It got 90*-95* 19 hr it never went over 100. So if you were to size it for the 95-100* temp. it would be sized correctley for the them 3 hr, but it would be oversized for the remainder of the of the season Thats why its based on 95*

    Hope it helps
    Anthony


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