New Trane XR14 AC Not Cooling Properly

[Rambo2000]

I have an 8 year old house with 2 Units (one on the main level and one upstairs). Each level has about 1750 sq. feet. The builder installed a 3 ton unit downstairs and a 2 1/2 ton unit upstairs (where the heat is, go figure).

After "fighting" with the upstairs unit pretty much since we bought the house (it leaked freon, never cooled properly, etc), we decided to have everything ripped out and replaced (new compressor, new coil, new line set). The original system was a 2.5 ton Lennox AC / Furnace system.

I had a new Trane 3 ton XR14 unit and 3 ton XTV Coil installed upstairs (retained the original Lennox furnace as we never had issues heating, just cooling). The contractor also identified issues with our plenum and ducts, so they replaced all of that as well (one of the reasons we chose the contractor we are working with is they asked if we had air flow issues which we did. They were the only ones to identify this issue out of 3 bids we had).

Unfortunately, the unit still is not able to achieve our desired temperature. As it gets very hot in Atlanta, I'm ok with (would like better, but can live with) the unit's performance during the daylight hours (recently, the outside temp hit 94 / 95 degrees, and the unit maintained 76 degrees indoors).

My issue: even 2 1/2 hours after the sun goes down and the outside temperature is in the low 80's, the inside temperature is still sitting at 76 degrees( basically, hasn't moved even though the heat load should've significantly decreased over 2 1/2 hours). Also, on a recent electricity bill, I've registered a 30% increase in the amount of electricity used by the new unit over the older less efficient Lennox unit (the old unit was 10SEER, but it leaked freon so I doubt that it ever got 10 SEER).

The contractor has "double sealed" and insulated all of the supplies and returns, yet, the air temp coming out of the supplies (as measured with a Raytek Infrared Thermometer is between 61 - 65 degrees during the day and the same 2 1/2 hours after the sun has gone down). The contractor says they've meased the temp at the coil at 53 degrees, yet, I'm losing 12 to 15 degrees in the supply lines.

The one exception is one of my children's bedrooms. The air temp coming out of the supply in this room is around 57 / 58 during the day, and this room is 2 - 3 degrees cooler than the rest of the upstairs (reads 74 when the other rooms read 76 / 77). There is a bathroom and another bedroom on the same side of the house (facing West) and they are both reading 76 degrees.

In the morning when I get up (around 5:00), the house is at 72 degrees (where the programmable thermostat is set), and the supplies are putting out air that reads anywhere from 53 - 57 degrees.

The unit is located in my attic with one attic forced exhaust fan set at 90 degrees. I measured the temp in the attic last night at 90 degrees when the sun had been down for 2 1/2 hours with the Raytek.

The contractor has been very pleasant to work with. They have added a supply in the upstairs hallway and added a return in one of the bedrooms that didn't have one. They have been out at least 6 times trying to get the system to perform as we all believe it should. They have looked at the system and claim it is functioning to manufacturer's specification, but even they agree that it should work better.

So, any ideas as to how to get my upstairs temperature down? Is it ?normal? to lose 12 to 15 degrees in air temperature between the coil and the supply vents? Am I asking too much to have the room temperature drop ( even a little!?!) 2 1/2 hours after the sun has gone down?

Any suggestions on things for the contractor or I to look at or advice would be greatly appreciated. I really don't mind investing in getting the home to be comfortable, I just want what I paid for to work.

Thanks,

Rambo2000

[beenthere]

Some Tranes units have had problems with the TXV.
They may want ot check it.

[Rambo2000]

Beenthere, thanks for the reply! I certainly don't want to insult the contractor as they have been very nice to deal with. They are meeting me there yet again tomorrow morning to look things over. Is there something specific I should ask them to check or just mention that I read on the Internet that the TXV valve on someof the Trane's have been problematic?

Again, thanks for your suggestion.

[beenthere]

Some TXVs have been found to have bad power heads.
So they don't open as far as they should.

They can also check to make sure the distributors of the evap coil to make sure its being fed evenly.
A restricted distributor tube can cause this, and will not always show up on the Sh, and SC readings.
Also, they should be checking SH, and SC, not just pressure.

If the coil isn't being fed evenly, its possible that where they check its temp is being fed right, and doesn't show the feed imbalance.

[BaldLoonie]

Cover the flex ducts all over the attic with more insulation. Whether it is blown over or cover them with batts, do something to keep the 150° attic heat out of the flex. That R4.2 insulation on the flex does little as you are finding. I have a 14" flex return that runs 20' and made quite a difference by wrapping it with R13 batts. Bury them in the existing insulation then lay batts on top or buy some bags and the home stores will let you use a machine to blow another 6" or more inches over them. Common problem and why I hate to see any ducts in the attic. Cooling the attic can help a bit too.

[beenthere]

The OP said the contractor double sealed and insulated the supplies.

[Rambo2000]

Beenthere / Baldloonie,

Thanks both for the replies. I will have the contractor check the TXV mesasurements you mentioned in the morning.

As to the isulation, the flex is suspended from the rafters and distributes out from the plenum. The insulation is just the ?normal? insulation that comes on the flex (I do not believe they added any additional insulation) but they did ?doubel wrap? the supplies and returns to make sure they were properly sealed. So, if I mislead you with what I said, my appologies (sorry, I'm a computer guy not a HVAC guy). I have a very high attic roof line above the top floor (say 20 - 30 feet at peak), so there is definitely a lot of heat trapped up there.

I can't bury the flex in the "blown-in" insulation the way it distributes off of the plenum, but adding batts might be an option. Would it just be a matter of cutting and taping the batts around the supplies and returns? Does anyone manufacture a product that might make it easier to add insulation?

Again, thanks to you both for taking the time to reply.

[forcryinoutloud]

Cover the flex ducts all over the attic with more insulation. Whether it is blown over or cover them with batts, do something to keep the 150° attic heat out of the flex. That R4.2 insulation on the flex does little as you are finding. I have a 14" flex return that runs 20' and made quite a difference by wrapping it with R13 batts. Bury them in the existing insulation then lay batts on top or buy some bags and the home stores will let you use a machine to blow another 6" or more inches over them. Common problem and why I hate to see any ducts in the attic. Cooling the attic can help a bit too.

I have experienced, that if you get your attic temp close to the dew point, and have flex ducts without an air gap around them, they will condensate on the outside and cause water damage to the ceiling.

We had a contractor that was building his own house that installed full length ridge vents, two large attic exhaust fans, R-30 batt insulation, then blew in 10" more of insulation on top of the batts. They covered our fiberglass trunks and flex ducts.

About 8 days after start-up they called saying that they had water streaming down the walls and it was coming from our ductwork. We moved the blown in insulation from around the ducts, set the stat higher on the attic fans, and all has been good since then.

That was the first time that I realized that you could actually over insulate and over ventilate an attic space.

[adrianf]

no matter what turn the PAV off

[Rambo2000]

adrianf,

Don't beat me up, but why turn off the PAV? I thought the idea was to pull the outside air through the soffets to get the heat out of the attic? Again, not trying to disagree, just a homeowner trying to understand?

Thanks,

Rambo2000

[RyanHughes]

Power Attic Vent.

[hvacsteve82]

Have you always had a power attic ventilator?

[beenthere]

That was the first time that I realized that you could actually over insulate and over ventilate an attic space.

It was over insulation or venting.
It was improper insulation of the ducts.

[adrianf]

adrianf,

Don't beat me up, but why turn off the PAV? I thought the idea was to pull the outside air through the soffets to get the heat out of the attic? Again, not trying to disagree, just a homeowner trying to understand?

Thanks,

Rambo2000

http://www.buildingscience.com/bsc/topten/south.htm
http://www.fsec.ucf.edu/en/publicati...sec-pf-406-98/


.3 Disabling Attic Exhaust Fan

The third retrofit involved turning off the attic exhaust fan. Average cooling energy consumption (based on an eight-month cooling season) decreased by an additional 36%. The 14.3 kWh/day saved breaks down to 11.2 kWh/day from the exhaust fan motor and 3.1 kWh/day from a reduction in air conditioning energy. Savings over an eight month cooling season are projected to be 3208 kWh or $289. Assuming a service call cost of $50 for turning off the attic fan, the simple payback would be after two months. Peak electric demand (including attic fan power of 0.47 kW) was reduced by 21% from 3.4 kW to 2.7 kW.

Impacts of Disabling Attic Fan on Ventilation, Humidity, and Building Pressure
Turning off the attic fan produced dramatic impacts upon the office. The large driving force (pressure differential) causing air conditioned air to be sucked out of the occupied space and hot humid air to be drawn into the occupied space is gone when the fan is off. Table 3 is located in the Conclusions section of this paper and summarizes measured ventilation rates, relative humidity, and building pressures during initial, duct repair, and attic fan off monitoring periods. The natural air change rate (all mechanical equipment off) is not shown in Table 3, but was measured on a couple testing days and averaged 0.17 ach.

Building pressure decreased from -0.064 in.WC (-15.9 Pa) to -0.0024 in.WC (-0.6 Pa). This resulted in a large drop in the ventilation rate and the indoor relative humidity. The 24 hour average relative humidity levels plummeted from 77% to 61%. Relative humidity levels are shown in Figure 4 during a composite 24 hour day consisting of one business week of data. Each hour represents the preceding hour of gathered data. For example, hour 2 represents data gathered beginning at hour 1 and ending at hour 2. Non-business hours from 12 AM to 7 AM show the humidity drop from an average of 83% when the fan is on, to an average of 65% when the fan was off. During business hours from 11 AM to 5 PM, the relative humidity drops from an average of 68% when the fan is on to an average of 55% when the fan is off. The building ventilation rate decreased from 0.79 air changes per hour (ach) to 0.33 ach. Due to diminished ventilation, the peak carbon dioxide concentration increased from an average 614 ppm to 1054 ppm during weekday hours of 3 to 5 p.m. Figure 5 shows carbon dioxide concentrations during a composite 24 hour day consisting of one business week of data.


Figure 4 Daily composite of indoor relative humidity before and after attic fan was turned off.

Figure 5 Daily composite of carbon dioxide levels before and after attic fan was turned off.

Measured ventilation rates and carbon dioxide concentrations indicate that this office needs additional ventilation after duct repair and with the attic fan off to be in accordance with ASHRAE 62-1989. Typical occupancy during normal business hours is eight adults. According to ASHRAE 62-1989, the desired amount of ventilation air would be 20 cfm (9.4 l/s) per person which totals 160 cfm (76 l/s) for eight people. Infiltration testing by means of tracer gas decay indicated a total of only about 58 cfm (27 l/s) or just over 7 cfm (3.3 l/s) per person. A suggestion was made to the building manager to contact a qualified air conditioning and ventilation contractor to increase the ventilation rate, but no changes were desired to be made by the business during the time that monitoring was conducted. It was not desirable to turn on the attic fan because it increased the relative humidity significantly. A discussion of how the ventilation could have been provided follows.

[adrianf]

http://www.natresnet.org/conference/...s_a_System.pdf

text taken from above link


The House Is A System
•Research at the Advanced Energy Corporation showed that 40%of the air exhausted by a PAV is conditioned inside air!

The House Is A System
•Convection loops move only 20% of the heat from the roof deck to the attic floor!
•Radiant heat transfer is responsible for 80%+ of the heat transfer.
•So, you could create Hurricane Katrina in your attic and only affect 20% of the heat transfer.

The House Is A System The House Is A System
•Lessons:
3.“Improve”attic ventilation and run the risk of making the house more humid, more likely to grow mold, cause the electric bills to go up and possibly cause a fire or CO poisoning!
__________________

[Rambo2000]

adrianf,


Thanks for the research! I did turn of the PAV. If I'm reading everything correctly, the Resnet conference seems to say turn off the PAV.

The building science article seems to indicate that venting an attic is a bad idea unless everything is done perfectly (I don't pretend to assume that my builder did everything perfectly), but I can't "unvent" it now and I'm also stuck with my air handler in the attic (also a bad idea). I don't see where this article said anything about the PAV?

The Florida Solar article seemed to indicate some reduction in heating by the PAV, but at a higher energy cost.

Of course, at this point in time, I'd take anything to make my conditioned space more comfortable. What is the typical cost for a radiant barrier system, and would it make sense in my case?

Thanks again for all of the insights!

R2000

[Rambo2000]

hvacsteve82


Yes. The builder installed the PAV

[pstu]

Price discussion is against the rules here, but I can say it is reasonable. You can get an estimate from a contractor easily enough, it will be a function of the square footage and complexity of your attic. It will probably be a special type of paint and will stop about 75% of the radiant energy. You could look into getting a proper passive attic ventilation at the same time, probably a ridge vent. In Texas there is a company named Efficient Attic Systems that advertises heavily and seems to be pretty good, one can hope they serve Atlanta too.

I put up foil type RB in my own complex attic and boy was it labor intensive! I like the results though they are hard to quantify. FSEC claims energy savings in the range of 8-12% and I believe them. With weather variations a savings of 10% is hard to measure (or even prove it exists). Most people are very pleased the attic is immediately more comfortable, too.

Hope this helps -- Pstu

[Rambo2000]

pstu,

Yeah, I should've known better than to ask about pricing on a public board (wasn't thinking).

I actually do have a passive system (soffet vents with a lot of daylight coming into the attic space, and a line of about (6 - 8) 12" square vents lining the roof line across the top. Not as good as a ridge vent, but something.

Out of curiosity, did you happen to measure your attic temps before and after the radiant barrier was installed? I'm curious as to what type of temp drop could be expected?

Thanks for your reply.

[VA GENT]

http://www.buildingscience.com/bsc/topten/south.htm
http://www.fsec.ucf.edu/en/publicati...sec-pf-406-98/


.3 Disabling Attic Exhaust Fan

The third retrofit involved turning off the attic exhaust fan. Average cooling energy consumption (based on an eight-month cooling season) decreased by an additional 36%. The 14.3 kWh/day saved breaks down to 11.2 kWh/day from the exhaust fan motor and 3.1 kWh/day from a reduction in air conditioning energy. Savings over an eight month cooling season are projected to be 3208 kWh or $289. Assuming a service call cost of $50 for turning off the attic fan, the simple payback would be after two months. Peak electric demand (including attic fan power of 0.47 kW) was reduced by 21% from 3.4 kW to 2.7 kW.

Impacts of Disabling Attic Fan on Ventilation, Humidity, and Building Pressure
Turning off the attic fan produced dramatic impacts upon the office. The large driving force (pressure differential) causing air conditioned air to be sucked out of the occupied space and hot humid air to be drawn into the occupied space is gone when the fan is off. Table 3 is located in the Conclusions section of this paper and summarizes measured ventilation rates, relative humidity, and building pressures during initial, duct repair, and attic fan off monitoring periods. The natural air change rate (all mechanical equipment off) is not shown in Table 3, but was measured on a couple testing days and averaged 0.17 ach.

Building pressure decreased from -0.064 in.WC (-15.9 Pa) to -0.0024 in.WC (-0.6 Pa). This resulted in a large drop in the ventilation rate and the indoor relative humidity. The 24 hour average relative humidity levels plummeted from 77% to 61%. Relative humidity levels are shown in Figure 4 during a composite 24 hour day consisting of one business week of data. Each hour represents the preceding hour of gathered data. For example, hour 2 represents data gathered beginning at hour 1 and ending at hour 2. Non-business hours from 12 AM to 7 AM show the humidity drop from an average of 83% when the fan is on, to an average of 65% when the fan was off. During business hours from 11 AM to 5 PM, the relative humidity drops from an average of 68% when the fan is on to an average of 55% when the fan is off. The building ventilation rate decreased from 0.79 air changes per hour (ach) to 0.33 ach. Due to diminished ventilation, the peak carbon dioxide concentration increased from an average 614 ppm to 1054 ppm during weekday hours of 3 to 5 p.m. Figure 5 shows carbon dioxide concentrations during a composite 24 hour day consisting of one business week of data.


Figure 4 Daily composite of indoor relative humidity before and after attic fan was turned off.

Figure 5 Daily composite of carbon dioxide levels before and after attic fan was turned off.

Measured ventilation rates and carbon dioxide concentrations indicate that this office needs additional ventilation after duct repair and with the attic fan off to be in accordance with ASHRAE 62-1989. Typical occupancy during normal business hours is eight adults. According to ASHRAE 62-1989, the desired amount of ventilation air would be 20 cfm (9.4 l/s) per person which totals 160 cfm (76 l/s) for eight people. Infiltration testing by means of tracer gas decay indicated a total of only about 58 cfm (27 l/s) or just over 7 cfm (3.3 l/s) per person. A suggestion was made to the building manager to contact a qualified air conditioning and ventilation contractor to increase the ventilation rate, but no changes were desired to be made by the business during the time that monitoring was conducted. It was not desirable to turn on the attic fan because it increased the relative humidity significantly. A discussion of how the ventilation could have been provided follows.

Adrian F....one of your links strongly suggested that in addition to disabling PAV's that a homeowner should close foundation vents which it said causes mold and mildew when open by bringing in hot, humid air ....is that also your recommendation? All the houses in my (Richmond, VA) neighborhood open foundation vents in the spring, summer and fall....sounds like we may not be doing the right thing ....?????