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Old 07-02-2012, 01:49 PM   #1
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HVAC for new addition


I have a 2800sqft single story house that was built in 2004.

After initial build i decided to finish out a 26x12 "bonus room" above the garage and put in a PTAC unit. It has gotten me by but because of a poor insulation job it has always struggled to keep up.

I am starting an addition to my house next week that will consist of roughly 900sqft of additional living space as well as 2 additional garage bays. Our master bedroom, bath, laundry room and a "florida room" will be the addition.

In order to make the budget I am doing pretty much everything but the framing myself. I have done everything but HVAC on prior projects ..... lack of experience has got me thinking extra hard about that part.

I have kind of taken a crash course and here is what I have come up with:

Goodman 3ton 16SEER 2 stage heat pump with a matching variable speed air handler. (DSZC160361A)(MBVC2000). I would prefer a 2.5 ton but with their dual stage units of this SEER rating they only go in full ton increments. I fear a 2 ton would be to small because of the potential heat load of the upstairs and the "florida" room that will likely be a revolving door for the kids during the summer time.

Jackson systems Z300 HPS zoning controller. Create 3 zones. Upstairs (removing the PTAC unit). Florida room. Bedroom/bath/laundry with t-stat in bedroom.

A single damper for each zone feeding multiple registers for each zone.

A static pressure bypass damper.

I have not decided on t-stats yet but they will be 2 stage capable.

I plan to address the insulation problems on the second floor at the same time I put in the new ducts.

Thoughts on the above?

It is my understanding that the 2 stage compressor will rely on the t-stats to let it know if the first stage is not keeping up. No matter if all 3 dampers are open .... as long as no single t-stat asks for additional cooling the compressor will stay in the first stage. I would not bother investing in a 2 stage compressor if this is not the case.


Last edited by swilk; 07-02-2012 at 05:08 PM.
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Old 07-02-2012, 05:06 PM   #2
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3 tons sounds large for less then 1200 sq ft.

Most zoning systems will let the stat decide if second stage is needed. Some will let you set it up that 2 zones need to be calling in order for it to go to second stage.

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Old 07-02-2012, 05:12 PM   #3
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Funny ... I was just editing my original post when you posted.

I agree that the 3 ton is big .... but Im concerned that a 2 ton might be to small. My wife and I spend a majority of our evening hours in that upstairs room .... its our hideout from the kids. 2 bodies, computer, television, light, DVD player, surround sound appliance. There is a bunch of heat load.

On top of that .... the additional florida room will have a potential to be forced to try and cool the outside air at times when the kids are running in and out.

So .... 2 ton or 3 ton?
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Old 07-02-2012, 05:57 PM   #4
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Might want o do a load calc, and find out what size you need for sure. It will also tell you how many CFM each room/zone needs, so that the duct can be sized right.

Many 3 ton unit, will actually be between 2.1 and 2.4 tons in first stage.
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Old 07-02-2012, 06:07 PM   #5
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If a guy actually buys a "Manual D" "J" books ..... recommendations?

Or is there an online calculator where a fella could enter the fields and those magic CPU's would spit out a value?

I looked at buying some software .... but man o man was that stuff expensive. I have no desire to make a living doing hvac work so I cant justify investing that kind of money.
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Old 07-02-2012, 06:10 PM   #6
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HVAC CALC its only 50 bucks for teh home owner's limited time license. Its duct design module leaves a lot to be desired though.

The ACCA website has the Spreads sheet to do both a load calc and a Manual D. they're free.
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Old 01-07-2013, 01:47 PM   #7
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Update and another question .....

After calculating out as much as I could I ended up going with a 2ton 16SEER 2stage unit.

I installed the Jackson Systems Z600 panel and set up 4 zones.

I have one higher end t-stat and three lower end stats .... the high end stat runs the bedroom zone and controls the stages for that zone. I jumped the stages together for the garage zone because it will be used very infrequently and when it is I want a rapid temperature change. The sun room and bonus room stats only run the first stage by themselves.

I am very happy with the system overall. We have had a colder than normal winter so far for southern Indiana and the heat pump alone is able to keep the addition warm.

I installed two outdoor t-stats .... one to lock out the auxiliary heat until the temperature falls below 10* and the second one to lock out the heat pump if the temp falls below 0*. So far the heat pump keeps up even when the temp is in the single digits. To my knowledge the aux heat has not come on with the exception of the defrost cycle.

The defrost cycle was set to a 30 minute interval from the factory ..... way to frequently. I played with the settings a bit and have finally decided that the maximum time (2 hours) works fine. If we have a stretch of weather in the high 30's-40* with high humidity I might adjust again but for now it is heating and ice build up between defrosts is not bad.

My one complaint is the air handler. The package I bought came with a Goodman MBVC1600 air handler which IMO is just to big for a 2ton system. I can slow the unit down to 1000cfm for the high stage but I feel it is still to fast. The air coming out of the vents is noticeably "cooler" than what comes out from my other heat pump.

My thought process tells me that the temperature coming out of the registers really doesnt matter .... more air moving at a lower register temp is the same as less air moving at a higher register temp.

Still .... it bugs me a bit.

Anyone familiar with these Goodman Air Handlers? From what I can tell the only difference between the MBVC1600 and the MBVC1200 is the blower motor itself. Everything else (cabinet, wheel, mounting brackets, control board, wiring harness .... everything) appears to be the same.

I sent a note to Goodman asking it I could swap out my motor with the 1/2HP ecm motor from the MBVC1200 and was told "no" with no explanation given.

Seems to me that if everything is the same between the two cabinets except the motor .... if a guy swaps the motor he should have a 1200cfm cabinet. If that was the case I can slow it down to more suitable speeds if I wanted.

I assume Goodman packages them that way to help with the SEER and other ratings ....
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Old 01-07-2013, 02:22 PM   #8
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Rather simplistic but can you choke it down by putting in a more restrictive pleated filter? Seems if you slow the air down a little it will be warmer from more time being heated?

Just a thought.
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Old 01-07-2013, 02:23 PM   #9
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I think the ECM motor would just spin faster to make up the difference.
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Old 01-07-2013, 03:30 PM   #10
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Did you set the air flow trim to -10%

What size and type of bypass did you install.
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Old 01-07-2013, 04:45 PM   #11
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-10 and I did not do a bypass yet. Neglected to order it when I ordered the rest of my stuff and just havent gotten around to it.

A bypass will mask the symptoms by recycling already heated or cooled air through the coil again making it even hotter or colder but it will still be 1000cfm for a 2 ton condenser.

I guess that isnt really masking the problem when the only problem is how the air coming out feels.

So ..... bypass it is and then Ill report back.

Last edited by swilk; 01-07-2013 at 04:49 PM.
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Old 01-07-2013, 04:58 PM   #12
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Can the zone panel control staging? You don't want to burn up that expensive VS blower because of too high of a static pressure.

Bypass damper prevents excess noise. And helps the blower move the needed CFM.

Do you have both Y1 and Y2 connected to the air handler.
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Old 01-07-2013, 05:10 PM   #13
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Zone controller can control the staging and that is what I was originally using to control the second stage. Last week I changed it over to let the t-stat control the second stage.

Until I get the bypass installed I will change it to only use the first stage ... which should be 670cfm from the blower. That shouldnt cause a problem with pressure through the zones being used this time of year ....

Excess static pressure will burn up a blower?
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Old 01-07-2013, 05:13 PM   #14
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I do have both y1 and y2 connected at the air handler ....
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Old 01-07-2013, 05:35 PM   #15
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Is 1000 CFM when it gets a call on Y2, or Y1. If Y2, disconnect Y2 and Y1. Leave the y1 from stat disconnected at air handler, and connet Y2 from stat to Y1. Set blower CFM so a Y1 call is 800 or 900 CFM.

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