Sizing AC Unit

[fmwaz]

We have just had our heating/cooling system zoned into 4 zones using a Honeywell Trol-A-Temp system. We are considering replacing the AC unit which is a 3.5 ton unit with a smaller one. I used the HVAC Calc Residnetial software(Great Program - Very Intuitive and Easy to Use) and came up with a total heat gain for the building as 33,789. The largest heat gain in any of the zones is 16,300. How do we size the AC unit? Since there is a foyer, there will be heat flow between the zone.

Thank you for the help.



[Edited by fmwaz on 05-17-2001 at 11:25 AM]

[Don Sleeth]

Hi, I believe there is one more piece of information I would like to add here. I spoke to fmwaz on the phone and he told me that the way the duct zoning works with this system is only one zone gets air at a time and the dampers are down at the furnace essentially blocking off 2 zones as one gets fed. I am not up on the Trol-A-Temp system but if this is correct, I would be concerned about putting in a 3 ton because there wouldn't be enough air flow over the coil. Can somebody with experience with the Trol-A-Temp system please reply and give me an education on how it works?

Thanks

don

[grampadip]

Originally posted by Don Sleeth
Hi, I believe there is one more piece of information I would like to add here. I spoke to fmwaz on the phone and he told me that the way the duct zoning works with this system is only one zone gets air at a time and the dampers are down at the furnace essentially blocking off 2 zones as one gets fed. I am not up on the Trol-A-Temp system but if this is correct, I would be concerned about putting in a 3 ton because there wouldn't be enough air flow over the coil. Can somebody with experience with the Trol-A-Temp system please reply and give me an education on how it works?

Thanks

don

I'v never worked on the trol-a-temp system but try this website http://hbctechlit.honeywell.com/.

[Dependableairservice]

zoning is basicly, a themostat controls each zone.
1 2 3
I'm concered when people want to change there units.
what if you want all zone's on the 3.5 cooled it all
if you drop to a 3 ??
i do get much work for this but have some ask an will
be getting into it more.

[srmfsr]

If his zone system shuts down all zones but one at a time, he's got problem with it. Just as Dependsaservice said the unit is controlled by a master thermostat and the other stats control dampers.

[BaldLoonie]

Each stat can bring on the equipment and open the damper for that zone. It is possible for a 3.5 ton unit to be feeding a duct designed for a fraction of that. Therefore, if properly installed, a bypass damper is used to return the excess back to the A/C. With Trol-a-temp's newest panels, they have a thermistor that goes in the supply and monitors for overheat or near freezing conditions to shut off the equipment before a coil freezes or a furnace cycles on limit. If the system does not have a bypass or the Zonemax sensor isn't used, he will have problems.

As for his gain, seems to me he has a 3 ton heat gain and when the A/C is changed, it should be to a 3 ton.

[Don Sleeth]

Thanks Baldloonie, the bypass damper was the piece of the puzzle I was missing. With that in place, then yes a 3 ton is what's called for or even save the expense and go with the existing 3.5 if it is a good working unit. His contractor was suggesting a smaller unit, I think because of the air flow, so I hope he was aware of the bypass damper. If he wasn't, I am sure he will be shortly

don

[bb]

Originally posted by r22d22
Read

Read What ?

[Milk man]

Originally posted by bb

Originally posted by r22d22
Read

Read What ?

Still lost yet again, but I can relate to your bio. in your profile.

[Milk man]

Hey, I like ideas, I even get a couple now and then. What's yours.

[rsmith46]

Originally posted by r22d22

Originally posted by bb

Originally posted by r22d22
Read

Read What ?

bb and lynn rodemayer don't know what to read.
(nothing)
A windows macro cause me to submit some strange entries without knowing it. But the replies were deliberate.
This gives me a great ideal.

Windows macro? Or drugs?

[Milk man]

Hey Mr. Smith. Which company do you work for? If you don't want to say, just reply bug off.

[fortressofcomfort]

"bb and lynn rodemayer don't know what to read.
(nothing)"

This is logically incorrect. What your are saying here is BB and Lynn know what to read. (everything)

Jeff