Increasing cooling in accessory apartment

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Old 07-03-16, 10:14 AM
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Increasing cooling in accessory apartment

I think this is simple issue with a simple fix, but just wanna confirm my plan.

First floor consists of 2 living areas: main living area ("Main"), and accessory (M-I-L) apartment ("Apartment"). Single doorway separating the two - door usually kept closed.

Each area has it's own t-stat, which controls it's respective hydronic heat zone. However....

The Main t-stat controls the A/C for both areas (i.e. one zone). The Apartment stat is not connected to the A/C system.

Problem: since the door is usually closed, the Apartment gets fairly warm - often 10 deg. warmer than the Main area. Keeping the door open for a few hours somewhat evens things out - but Mama likes her privacy.

Presuming the Apartment t-stat was just never wired to the A/C system:

1. Can I just run 18/2 wire (G-fan and Y-compressor) to the air handler?

2. Do you think I'll need 18/3 - to add a R to go to the air handler transformer? (suppose I'll know that when I take the t-stat off the wall).

Since there's already wires from the Apartment t-stat down into the basement, fishing should be easy. Just wanted to think this out loud with y'all.

Thanx!! Wally
 
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Old 07-03-16, 10:20 AM
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The Main t-stat controls the A/C for both areas (i.e. one zone). The Apartment stat is not connected to the A/C system.
Do you have two completely separate A/C systems.... two outside compressors and two inside air handlers ?

My guess is you only have one A/C system which means only one thermostat can control it.
 
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Old 07-03-16, 10:52 AM
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Ahh...I didn't know that. I suppose that's why only one of the t-stats is wired to it (only 1 system). I (ignorantly) thought I could wire them both to it, and it would come on when either of them called for cooling.

See, this is why smart DIY'ers come here first...

Thanx!
 
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Old 07-03-16, 10:56 AM
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Yes.... technically you could have two thermostats controlling one A/C unit but if either was calling for cool.... both areas would get colder. (not quite helpful)
 

Last edited by PJmax; 07-03-16 at 11:19 AM.
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Old 07-03-16, 11:09 AM
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Connecting 2 thermostats to a single air conditioner can often result in a back feeding issue, through the G terminal, that can cause ice to build up on the indoor coil.


Does the main thermostat have a C wire?

The Honeywell VisionPro TH8110R would allow you to add a wireless sensor and take an average reading of both areas to control cooling.
 
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Old 07-03-16, 11:11 AM
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Yup, I see your point. If the Apartment cools to 76 deg - then the Main area will go far below that (brrrrrrr.....).

'Suppose Mama's gonna have to sweat a little.

I wonder if I can do a little creative dampering / ducting...hmmm...

Thanx again!
 
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Old 07-03-16, 11:15 AM
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Adding a return air duct might be something to look into.
 
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Old 07-03-16, 11:24 AM
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Sorry Houston - just saw your reply...

Not sure if it has the C wire. Still working this issue in my head (actually, for 10 years now..LOL). haven't pulled the Apartment t-stat off the wall.

Definitely will look into that VisionPro! Sounds like the perfect solution.

Thanx!!
 
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Old 07-03-16, 11:33 AM
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Definitely will look into that VisionPro! Sounds like the perfect solution.
A solution.... but not the perfect one. It will still be a compromise.

The ducting solution would be closer to what you want.
 
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Old 07-03-16, 11:34 AM
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Yup - both areas have their own returns.
 
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Old 07-03-16, 11:46 AM
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I didn't mention this - 'cause I (incorrectly) thought this was an easy fix - but here's the main problem (i.e. reason why the Apartment gets so warm):

The Main living area is 2-story, but the Apartment is 1-story, with an almost-flat roof (i.e. there's no 2nd floor to 'shield' it from the sun. Plus, the Apartment has a sliding glass door that the sun blasts through in the afternoon. I tried the radiant-block film on the glass - didn't make much difference.
 
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Old 07-03-16, 11:48 AM
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Then you may need some more supply into that apartment.
 
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Old 07-03-16, 01:37 PM
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This is an excellent discussion, and EXACTLY why I love this forum.

I have many more thoughts / questions, and want to continue - but since we've (more or less) resolved my initial topic, I suppose I should start a new thread. It'll be something like "Adding cooling to accessory apartment"...so if y'all could look for it, we can continue. I'll start it shortly.

Thanx again to all!! Wally
 
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Old 07-03-16, 02:17 PM
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Increasing cooling in accessory apartment

This is a continuation of a discussion I started in another thread. Essentially, I'm trying to increase the cooling in an accessory apartment. Background:

Modular home, built 2005. Oil / Hydronic heat, central A/C. This discussion really only concerns the first floor A/C (3 ton Heil):

First floor consists of: main living area ("Main") approx 1100 sqft, and attached accessory (M-I-L) apartment ("Apartment") approx 650 sqft. Separated by single door.

Each area has it's own t-stat for their respective heating zones, however, the A/C is one zone controlled by the t-stat in the Main area.

Main area is fed by 7 branches, either 6" or 7" flex-duct. Apartment is fed by 4 branches, same size flex-ducts. Both areas have their own returns.

Problem: Apartment gets significantly warmer than the Main area. Main t-stat set to 76 deg. and A/C does a reasonable job of maintaining that. Apartment can get as high as 85 deg. in the late afternoon. Reasons: Apartment is mostly 1 story (i.e. no 2nd floor to shield it from the sun) - with a fairly flat roof (I think 2/12, and no venting for crawl space above). Plus, there's a sliding glass door which gets blasted by the afternoon sun.

I have applied radiant-blocking film to the sliding glass door (not much help), and I think adding some gable-end venting to the crawl space above to get rid of some of the trapped heat may help.

From the previous thread, we determined the single A/C zone can only be controlled by one t-stat, so "linking" the t-stats needs more investgation.

We also mentioned somehow adding 'flow' to the Apartment, but I have some concerns:

1. Should I increase the flex-duct diameter (10"??).
2. Should I add another branch(es) to the apartment?
3. Will I need to increase the return diameter (for proper balance)?
4. Will the 3 ton unit be able to provide the increased flow?

Good discussion. Thoughts anyone?

Wally
 
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Old 07-03-16, 02:24 PM
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Wally... no thoughts at the moment but I combined your threads into a single topic. Flows better and keeps all the ideas in a single place.
 
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Old 07-03-16, 02:34 PM
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Agreed...makes sense. Thanx.
 
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