Conflicting HVAC advice...too funny

[BMWTurboDzl]

Scenario: Zoned system.

For those who haven't heard of this. It's a system where the trunk line for each floor has an internal damper that opens and closes via motor. The system also has another damper that is simply weighted and vents excess air pressure ( 1 zone running this vent lets more air escape vs when 2 or more zones are open).

The disagreement : initially this vent line was run back into the HVAC via box that the a return was attached to. In this set up we would get cold air out of the 2nd floor return.

System was modified to disconnect this line from the box and let it vent into the attic as waste air.

Why? Well here is the disagreement. We lost our compressor and supposedly it was because under the initial configuration freon wouldn't change into a gas when it hit the evaporator coil due to the recirculation of conditioned air. The liquid freon would return to the compressor and it eventually killed it. With the vent line off the return the freon returns to a gaseous state and we get better efficiency as well as prolonged compressor life. However we're venting cooled air into attic (waste).


Different HVAC guys will say that one configuration or the other is incorrect. There is no agreement on it.

 

[JHZR2]

HVAC is one of the shadiest businesses Ive engaged with. I have no doubt each is lying just to sell you extra work and billable hours.

 

[antiqueshell]

Originally Posted By: JHZR2
HVAC is one of the shadiest businesses Ive engaged with. I have no doubt each is lying just to sell you extra work and billable hours.


Agreed, residential HVAC and automotive repair are two of the most dishonest and money grubbing businesses, and yet you always hear many of these businesses whining about how they get the bad reputation which is undeserved, but the dishonest practices continue on without the industries doing anything to curb the problems. LOL

What a joke.

 

[bepperb]

There is an acceptable temperature differential between the supply and the return. For heat at least it's listed on the sticker inside the chassis, for A/C you might need to find some paperwork. There should be a hole in each and you can get a thermometer to shove in there to see what the actual differential is. This should have been done to verify that first hypothesis.

Why listen to two contradictory workers and then ask a bunch of internet users to guess after providing no data... when you can find out exactly what the situation is.

 

[JHZR2]

Originally Posted By: antiqueshell
Originally Posted By: JHZR2
HVAC is one of the shadiest businesses Ive engaged with. I have no doubt each is lying just to sell you extra work and billable hours.


Agreed, residential HVAC and automotive repair are two of the most dishonest and money grubbing businesses, and yet you always hear many of these businesses whining about how they get the bad reputation which is undeserved, but the dishonest practices continue on without the industries doing anything to curb the problems. LOL

What a joke.


And the problem is that there ARE absolutely phenominal folks in both areas.

 

[BMWTurboDzl]

Originally Posted By: bepperb
There is an acceptable temperature differential between the supply and the return. For heat at least it's listed on the sticker inside the chassis, for A/C you might need to find some paperwork. There should be a hole in each and you can get a thermometer to shove in there to see what the actual differential is. This should have been done to verify that first hypothesis.

Why listen to two contradictory workers and then ask a bunch of internet users to guess after providing no data... when you can find out exactly what the situation is.


Oh I'm not questioning just pointing out something which I thought was humorous.

 

[EA82]

Zone systems are something that I don't see a lot in new construction anymore, they just install a separate split system instead, they can be tricky at times. Mechanical damper is there for the rest of the air to escape when only one zone is running, dumps the rest of the air back in the return. Just blowing it in the attic is doesn't make any sense, the duct with the mechanical damper was not installed properly in your case, it should go to the return plenum instead of return box. Maybe your application doesn't allow it im not sure. Zone systems can be a pain in the neck with high efficiency communicating units.

 

[UNC017]

A zoned system like that really needs a two-stage condensing unit to go with it. That way when the diverter dumps cold air back into the return, the capacity of the system throttles down and you actually save energy. "Slugging" a compressor with liquid refrigerant is a bad thing... but there are ways to deal with it (staged compressor operation, liquid accumulator / vapor separator in the suction line, for example!) and the idea of dumping expensively conditioned air into an attic space as "waste" is just crazy. Just think about it: by doing that, you're still spending as much money on power as if you were cooling the whole house. You're getting NO benefit from the zoned operation whatsoever. Maybe worse than that, since hot air has to be pulled into the house to compensate for the cool air dumped into the attic.

 

[EA82]

To add to that, the excess air duct is also dumped into another area into the house like foyer or some place where it's not controlled by the zone, to prevent cold air going back to the return, but than again with only one zone running you would starve the unit of return air, which could cause it to freeze and damage other components like blower motor . Im just not a fan of zone systems.

 

[BMWTurboDzl]

Originally Posted By: 440Magnum
A zoned system like that really needs a two-stage condensing unit to go with it. That way when the diverter dumps cold air back into the return, the capacity of the system throttles down and you actually save energy. "Slugging" a compressor with liquid refrigerant is a bad thing... but there are ways to deal with it (staged compressor operation, liquid accumulator / vapor separator in the suction line, for example!) and the idea of dumping expensively conditioned air into an attic space as "waste" is just crazy. Just think about it: by doing that, you're still spending as much money on power as if you were cooling the whole house. You're getting NO benefit from the zoned operation whatsoever. Maybe worse than that, since hot air has to be pulled into the house to compensate for the cool air dumped into the attic.



In all fairness when the system runs it usually calls two zones at the same time. When that's happening very little air is getting dumped as the bypass damper is essentially closed. TBH I'd rather burn an extra $20/mo vs thousands for a new system that goes into a house that leaks like no tomorrow (almost none of the windows are square and there a major gaps around exterior doors (Production builder half[censored] framing).

In any case you're right about the 2 stage. Unfortunately we had our condenser replaced under warranty about 4 years ago so we're not in the mood to spend a ton of $$ on an already poorly designed system. The duct work is completely jacked up (production builder sub circa 2000). There's no way to balance the air on both floors because the boxes aren't readily accessible. We were supposed to have moved into a house back in '04 but job losses and the RE crash in '08 put the kibosh on that.

We rarely run the third zone so I've toyed with the idea of dumping the excess air into it. That however would require some serious carpentry as I would have to block off half of the third floor and take down the wall in the utility closet to make room.

 

[sleddriver]

So you have three floors (stories) being handled by a single unit? Did I read that right? If so, that's nuts. Especially in Atlanta. So is dumping expensive, conditioned air into the attic. Doing so causes warm, humid, unfiltered air to be drawn in through the cracks you mentioned.

I'm also guessing your system doesn't use a TXV (thermostatic expansion valve), as it meters the flow of refrigerant into the evap coil depending upon its temperture (using local feedback). This in contrast to the cheap capillary tubes which spray the same amount of refrigerant regardless.

I had my system refitted with a TXV a few decades ago as it's more efficient and protects the compressor from this.