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## calculating the charge

I had my problem since two years now. A lot of contractor has passed throught and no result.

I have two floor around 2000 squared foot. They put me a 5ton on each floor.

During each day, the temperature is not constant. Sometime is hot, sometime is hot. This feeling came 2 or 3 time per hours.

A lot of research has been made, and the final answer came that my hvac is too big for each floor. So they came with the idea to change the two hvac system with one bigger.

The problem is there calculation of the charge is very strange. Since the begenning is my fourth set of cooling charge and they doesnt seem to take all the variables to calculate the real charge

Lets take my own office (187 squared inches, 1683 cubic feets ).

They say that i have a charge of 7606 btu per hours. It's more than an half of ton.

Here's how they have determined the btu

Lightning : 1276btu ( i have four led light of 40w each(
Person : 900btu ( i am only one working in this office)
Computer : 1200 btu ( one computer with two screen)
New air : 913.2 btu
Windows : 3317 btu ( 39 square inches, solarband facing south east,montreal quebec)

can you tell me if theres calculation is good or not

Two 5 ton packaged one piece units? for a total of 2000 square foot house or each floor is had a 5 ton unit for 2000 sq. Foot?

Who are these people looking at your job and making suggestions? Did you get several other bids and options/recommendations?

“ A lot of research has been made” such as, and by whom?

A/C system is only as good as the ductwork ( sized correctly for a correct load ) delivering the air.

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no its a commercial building
two floor of 2000 sqare inches each

4. What country is this for?

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we have deal with 3 contractors, engineer.

first floor is 2000 square feet with 7 rooms
second is 2000 sqaure feet with 5 rooms.

Every try they have made doesnt correct the problem.

For my exemple it was only one room of the seconde floor

7. Originally Posted by BOBDION
no its a commercial building
two floor of 2000 sqare inches each
Rooftop units packaged units ? side wall packaged units? split system ducted units? how's your system layed out? Sounds like duct issue was not designed correctly if new duct system, if existing, why wasn’t any modifications made?

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york ze060h ( rooftop)

9. What’s the history of these units, you inherited existing systems? Are these brand new RTU’s and brand new ductwork? If the RTU are located on the roof then the ductwork to the 1st floor must be exceedingly long runs? If existing system and duct, chances you would need duct modifications at the very least?

If new system shouldn’t the installing contractor try to straighten things out?

“The problem is there calculation of the charge is very strange. Since the begenning is my fourth set of cooling charge and they doesnt seem to take all the variables to calculate the real charge”

You mention cooling charge, RTU packaged one piece units come precharged from the factory, there would be no reason to mess with the charge on new units?

Even if these systems where used/original to the building before you moved in, the factory charge is listed on the electrical data plate.

“ For my exemple it was only one room of the seconde floor”

You would think if there is any problem it would be the 1st floor, if they installed these packaged units on the roof?

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everything is new, i think the work was cheap and fast.

But the new guy knows everything, and if we have to redo things, i will do. But they try and its doesnt work.

The last test they did was to control the economizer. To keep my ac at 13 celcius, on a hot day, they have to open it near 100%

why i say theres is a problem if the ac goes below 8 degree celcius, and cut off on protection.

Also too cool down from 27 to 22 its take 18 minutes, with outside temperature at 38 with a lot of humidity.

11. Probably what I would do is get couple load calculations to compare to see what you need, including heat if these are gas units also. Then take it from there. Have someone look at your ductwork to see if it’s sized correctly ( if you want to join together and use one packaged unit ) and to make sure it has enough balance in dampers or whatever to use to make sure Air gets to the 1st floor.

You never mentioned why these Contractors where messing with the charge, when they come from the factory charged correctly?

If you have to run the econimizers wide open to bring in a false load to keep your system running that speaks volumes about the sizes of your system. Do you have trouble with outside doors closing? as with economizers wide open, and no exhausting of the air inside, you must have a over pressurized building, no??

13 degree C is around 56 degree F so what are you trying to control to keep something 13 degree, or are you talking about your discharge air temperature being 13 degree?

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what i mean by charge is heat and cooling load

13. Originally Posted by BOBDION
what i mean by charge is heat and cooling load
You got me on that statement? Others here can help...IMO as mentioned start from the beginning, get a accurate load calculation then take it from there, and have a professional who knows duct sizing to check your existing ducts once you figure out the actual tonnage needed for any possible recommendations....