[dorlando]

Hello,

I had a 3.5 ton single phase unit installed in March. I can’t put my finger on it but I have this feeling it is not more efficient than the previous 19 year old unit and possibly using more power. A tech has recently looked at it and said static pressure was .41. He also said my subcooling was 1 and needed to be between 5 and 7. I then had the installer come out and he said subcooling was fine. My split at plenum and return is 20-21 in early morning and night and 19 during the day

When I called the field manager of the tech who said subcooling was low he said based on your split his reading must be wrong, so he didn’t suggest more freon. So I now wonder if the static pressure reading was wrong too

I have an overhead return from hot attic and a direct return from the house so my return temp is blended. On past 90 degree days the overhead return is 84.4 degrees and direct is 79, the temp we keep the house at. The plenum temp is 61. Due to the blended return temp the split is at least 19 on a hot day

Yesterday I checked the plenum temp after running for at least 10 minutes and it was 63.6. The vents in the house were a couple degrees warmer than normal too. The temp outside was 89/90.
I checked plenum a few minutes later and it was 62.3. This was after running for at least 15 minutes

It started raining so temp outside cooled down and on next cycle plenum was 61. Later that night, 9:30 pm, plenum was 59.

I used a lot of energy in the house yesterday and I have never measured 63.6 at the plenum before. Can the overhead return cause fluctuations in the plenum temp? Can there be a wiring issue causing the unit to use more power than necessary?

Something isn’t right but two people have been out here. Is it possible for something else to cause fluctuations in plenum temp? My two concerns are power consumption and temp out of plenum. Thanks

 

[dorlando]

I don’t disagree with you. I am going to check the return duct this weekend. I just took some measurements of the temperature. Overhead return was 77. Direct return 79, room temp. But temp in filter rack was 75. Is it possible for the temperature in the box to be less than the return? Plenum was 57 after 8 minutes and 55.7 after around 13 minutes. So split between 19-20 depending on how you read the return air.

Is there a wiring connection or something that can cause it to use more power? I am basically just watching my power used each day and comparing similar days with similar power usage around the house

 

[dorlando]

Agree. I’m only going off of friends who say they saved with a new unit and I think that is what one would expect when replacing a 19 year unit. One difference is the thermostat. I now have the Honeywell pro 8000. So far I’m not a big fan of the learning thermostat. It keeps the house tighter and more comfortable and that could be contributing to more power usage. It replaced a stat with a 1 degree temp swing and the pro seems to come on when I don’t think it should and not come on when I think it should. I have changed the cph to 1 because it was cycling on off too much. I am thinking of going back to a non learning stat

 

[dorlando]

I really appreciate your help, this is something that has been keeping me up. To be honest, I am just looking at kwh used on similar days with similar power usage around the house. I know that isn't the best method but it is all I have. My thermostat doesn't keep a usage log. When the tech came out he did check the amps, I think amps, on the air handler and he said it was within range. The only thing he noted was the subcooling was off but the field manager said if my split is 19-20 then he wouldn't put freon in it.

I think I do need to address the return air but not sure how to. I will check for leaks but assuming there is no leak is throwing some insulation batts over it helpful?

I am still puzzled by the plenum air temp being 63.6 yesterday early evening when it was around 89-90 outside. I have never measured it over 61 before and that was on a hotter day. The 63.6 was after the unit was on for at least 8 minutes. Later that evening after it rained the plenum temp dropped to 58-59 and this morning it was 57. I think my split is still 19-20 but hard to gauge because I have blended return air (from attic and straight from the house)

Is there something that can be delaying the coils and keeping them from cooling down faster than they are?

 

[dorlando]

Does the inside humidity impact the coil discharge temp or outside? The inside reading has been averaging around 54 during the day lately as we have been getting a lot of rain. I live in Florida. However, in the evening the reading goes down to around 50.

 

[dorlando]

Old unit was a 3.5 ton and same with new unit, it is a matched unit and replaced at the same time. Not sure what the manufacturer recommends. The tech only said that subcooling was low but the field manager said that isn't possible with a 19-20 split so they didn't add anything. The other thing he said is that evaporator coil is 44 degrees and he likes to see it at 41. If humidity impacts the discharge temp then maybe I should expect to see a slight drop in the split?? I'm just not sure if I need to pay someone to come out again. I am going to take more readings throughout the day today but humidity is around 54 right now in the house.

I think I am going to go back to a non learning tstat, one also with a larger swing so I can get longer run times.

In regards to humidity, sometimes our humidity will decrease and sometimes it doesn't when the unit is running. Yesterday during the day it didn't come down by much but after 7:00 pm it started to come down. I'm not sure why that is.

 

[dorlando]

I understand. is there anything else I can add to help you? When I called the shop manager about the readings he said that it is probably a bad reading and since the split is good he would not advise putting any freon on.

 

[dorlando]

4HP15L42P-50 condenser
BCE5C42mA4X HP - air handler

I was told it did have a TXV valve. WHen the installer came out to check the unit it was showing a low subcooling but he said it was because the valve was closed or open or something like that. The subcooling eventually leveled out, according to him.

 

[dorlando]

Thats awesome, Thank you. It is a concord unit. yes, subcooling is on the unit panel. The first tech read it and it said it should be between 5 and 7. He was getting 1 and he wanted to add a pound in. Since the unit was fairly new we agreed for me to call the installer. The installer came out and said subcooling is within range. I then called shop manager of first tech and he said he must of been a bad reading if my split is 19. The blower speed is on medium. I will say my airflow is much better than old system but they also made a couple of tweaks on the plenum connection.

I personally don't think they did a very thorough job in setting it up which is why I am having to be here. Unfortunately they said something different than the tech in regards to subcooing. I may need to just ask around and have someone come out who has never looked at the system before.

Question, if they tell me that since my split is between 17-22 then all is good how should I respond? My split is in that range but it has decreased a bit recently but maybe due to high humidity in the house. I think the unit may be a little oversized and I need to switch to a different tstat as the pro 8000 isn't running long enough as it keeps things tight. If it is oversized a little a larger swing may help with humidity.

Lastly, I think this may be a 4 hp unit. Is it possible that it is more hp than my older 19 year old 3.5 ton and if so would that consume more power?

 

[dorlando]

Yes. He showed me the plate but when installer came out he said it was within range, actually a little higher maybe. To be honest, not sure if I have faith in either of them. Unit is 3.5 ton. I didn’t know if maybe it has more hp than older unit.

I think one of my issues is my overhead return coming into the box at 84 degrees. It was also there with prior system too.

 

[dorlando]

It was coming on for 10 minutes and off for a few then again on. My first bill was higher than last year. Unit was running a lot. I’ve read on this site that you want some longer run times to remove humidity

 

[dorlando]

Also, when unit was installed it was pre charged with refrigerant. I know the installers did not put any more in because they told me. They said since it was only a 28-30 foot run then what it came with is enough. They said the readings they got supported that.

 

[dorlando]

oh wow. It says pre charged for up to 15 feet. I have read that sheet before but never noticed or paid attention. Maybe they did put some in but I don't think so. When they came out again they made it sound like it didn't need it due to the length of the run. I need to find someone I can trust to come check it out. One other question, I am having trouble reducing humidity. It has been hanging around 54%-55% during the day and come late evening it drops to 51 and stays there until the morning. Several weeks back it was around 50% during the day but we have had a lot of rain the last two weeks. The cycles are usually under 20 minutes when it is 92%. I think it is a bit oversized but all 3 companies said a 3.5 ton and at least one said they did a heat load calc. I live in Florida.

 

[dorlando]

What is ID temperature? I couldn’t find it

 

[dorlando]

Thank you both so much. I have it on medium for the blower speed. I would like to kind of set it on low but I’m concerned about making sure enough air blowing over the coils. The airflow in the living room where the thermostat is is extremely strong. The cycles are really about 20 minutes when it’s 93° outside. This is why I was also looking at getting a thermostat with a swing temp to try and lengthen those cycles a little.

 

[dorlando]

true about the swing. I have a call into a reputable hvac company. Although I might be a little under charged I am wondering if the big issue is the overhead return bringing 84 degree air into the return box on a hot day. I just checked the split at 9:00 am and I am getting 57 out of the plenum and 77 out of the return. Once it hits 90 degrees that will change to 62 out of plenum and 81-82 of out return. My split is still 19-20 but I know have 62 degree air going through the attic picking up heat and discharging at the vents at 65-66 on the far side of the house. That leaves a 13 split in that room if we can stat at 79.

I assume if I am a tad under charged that may help a degree or two but wondering if the bigger issue is the overhead return.

 

[dorlando]

Hello, no, the return ducts were not changed. Is it possible that the new Concorde unit is drawing more amps than my prior unit? I have read that the unit draws the most amps at start up. This unit does cycle much more often than our prior unit. Our prior unit would run for much longer periods of time instead of cycling a couple of times an hour like the new one does.

The older unit would run for an hour or more at a time. The new unit doesn't run for more than 30 minutes at a time but on a 90 degree day it is about 22 minutes. Since it is cycling more often about how much more energy can that equate to?

Also, when the tech comes out what are the main things he should like out to be sure the setup was correct, other than the charge of the system? Is there anything at the air handler?

 

[dorlando]

I’ve been reading other posts on here about cycle times and how longer cycles are more efficient. My older unit would literally run for an hour or more at times. My current unit definitely cycles more. Yesterday it was 90 degrees max and the unit came on every 17 to 25 minutes and ran for 15-20 minutes. The ranges are due to change in outdoor temperature between 84-90. Does that sound normal? We get full day sun

The new unit cycles quite a bit more. While it may be within norm is that causing a higher energy usage since I am not getting the long cycles?

 

[dorlando]

While I may not disagree I have read that 15 minute cycles is mild 85 degree weather is normal and that one to two cycles per hour is normal. It is same tonnage as prior unit but a tweak was made to the plenum to probably more airflow. The prior unit had hot spots in a couple of rooms.

I will say the overall comfort level is much better now. With a more narrow swing on the stat we are more comfortable. I understand with comfort comes an expense.

I was just trying to understand cycle times. I have read longer times are better but have also read 15-20 minute cycles are normal for 85 degree temps

 

[dorlando]

This is with the stat at 79 so maybe not so much oversized considering design temp setting is probably lower