HELP with deciding units.

[ahubley09]

I originally posted a couple days ago and a single zone system vs two sone system with 2 and 3 tons cooling, but after I received a heat load calc my original thoughts were way off.


I am currently construction and would like to get a couple opinions from this board on which way I should go. From the heat load test it is showing a 1.5 ton (downstairs) and 2 ton (upstairs), but I would like to install the infinity but I am told they don't make one less than 2 ton. What is Trane's comparable system?

I would like to get a couple opionions on this load test. Any help would be appreciated.

See attached load calc.

[beenthere]

Trane 2 ton 20i. Its only 1 ton in first stage.

[dan sw fl]

Is a zoned 3-ton unit do-able?

98'F design temperature may be a bit conservative.

[motoguy128]

Is a zoned 3-ton unit do-able?

98'F design temperature may be a bit conservative.

Most likely, yes... especially with a more conservative design temperature. Plus, one advantage is that you can upsize the ductwork upstairs to handle 1200CFM and have the ability to cool it off relatively fast during recovery periods if they don't overlap. If both floors are sized for full capacity you don't need a bypass damper.

I still prefer 2 systems overall... but in this case, if you entertain a lot, a zone system would have the advantage of extra capacity for downstairs when you have a lot of guests heating up the house and you cooking without a "penalty" of being oversized the rest of the time. 1.5Ton could be pushed hard with a lot of guests.

Also, with relatively small system overall, you could plan for future zones to be added. SO a master suite, kitchen/dining room and other large rooms could be seperated into a different zones if you plan the ductwork carefully and size if for at least 600 CFM in that zone, then use a XL20i.

[ahubley09]

Most likely, yes... especially with a more conservative design temperature. Plus, one advantage is that you can upsize the ductwork upstairs to handle 1200CFM and have the ability to cool it off relatively fast during recovery periods if they don't overlap. If both floors are sized for full capacity you don't need a bypass damper.

I still prefer 2 systems overall... but in this case, if you entertain a lot, a zone system would have the advantage of extra capacity for downstairs when you have a lot of guests heating up the house and you cooking without a "penalty" of being oversized the rest of the time. 1.5Ton could be pushed hard with a lot of guests.

Also, with relatively small system overall, you could plan for future zones to be added. SO a master suite, kitchen/dining room and other large rooms could be seperated into a different zones if you plan the ductwork carefully and size if for at least 600 CFM in that zone, then use a XL20i.



I would like to stay with the two unit systems. Would it be effective to go with a 1.5 and 2 ton units, a 2ton and 2 ton, or a 2 and 2.5 ton system?

[motoguy128]

I wouldn't oversize. If you go 2 ton downstairs, go with a 2 stage. But don't just oversize it. If you know you have company comming over and it's near desing conditions outside, you can alwasy drop the temp a couple degrees ahead of time. The unit running constantly will pull out a lot of humidity so eve if it climbs a few degrees you'll still be comfortable.

Also, the upstairs will remove most of yoru humidity on hotter days. SO the downstairs unit, could be set to a higher CFM setting to get a little more sensible capacity, but still use dehumidify on demand to return it to normal airflow when it's more humid. But you'll need to make sure the ductwork can handle a little more capacity.

In the end, you have a really well insualted home.

Remember with well insualted homes with relatively small AC systems, they won't change the temp as quickly as you might be used to since you still have a large volume of air to cool and all the interior furnishings, walls, flooriing, etc. So you can't use large setbakcs and expect it to cool off quickly. At most you probably only want to use a 3F setback. But you'll find that a well insulated home of descent size will only gain 2-3F all afernoon even on a hot day. So it goes both ways.

[motoguy128]

Just curious, but how does a single system come up with about a 5% larger load than 2 systems?