Rheem R410a System

[docholiday]

Are you running any ype of exhaust fans or attic fans that might be casusing an air change? Has the return been inspected in the attic?

You got outside air getting into the home somehow, thats my best guess.

[ms7168]

The return was inspected. They told me when they put the system in that we surely did not want any attic air getting into the works.

I have noticed something that happens every time. When the supply air temperature goes up the humidity goes up and then when it comes back down the humidity comes back down. Does that make any sense? If it is a day where the supply air temp doesn't change much the humidity doesn't either.

[docholiday]

Are you running the fan continuously? If so...STOP IT.
What are the dry bulb temps?



[Edited by docholiday on 07-23-2005 at 09:40 AM]

[ms7168]

No, I don't run the fan continuously. When the thermostat kicks on the air the condensor comes on first and gets the coil cold and then the fan comes up gradually. When the thermostat kicks it off the condensor shuts down and then fan stays on for 45 seconds and then shuts off gradually.

Dry bulb supply = 57
Dry bulb return = 66

[dash]

Originally posted by ms7168
No, I don't run the fan continuously. When the thermostat kicks on the air the condensor comes on first and gets the coil cold and then the fan comes up gradually. When the thermostat kicks it off the condensor shuts down and then fan stays on for 45 seconds and then shuts off gradually.

Dry bulb supply = 57
Dry bulb return = 66

Are you sure ,return 66°?

[ms7168]

Yes, I didn't believe it either. But that was this morning. Right now it's 100 outside with a 68 dewpoint and my dry bulb supply = 64 and my dry bulb return = 73

[dash]

That's only 9° difference,assuming you are teating at the grilles,try testing at the inlet and outlet of the equipment.


Higher return there would indicate duct leaks pulling in warm ,moist air.

[ms7168]

OK.

Inlet Return Dry Bulb = 74

Outlet Supply Dry Bulb = 64

Thermostat is showing that it's 73 in the house but the other thermometers in the house are showing 74 and 75

I typically see a 9 to 12 degree difference between supply and return. Isn't that about right? Assuming the unit is always running.

[docholiday]

I'm lost... 66 DB? 73 DB?

Tell you what, get the wet bulb and dry bulb temps at the same place within a few minutes of each other.

Preferably at the unit but at the grills is ok too, in fact, get them in both places. Both wet and dry.

Return Grille
Return of indoor unit
Supply at indoor unit
Supply at register

Sorry but something isnt making sense here.

[ms7168]

I've been taking these temperatures at various times through the day as they have been requested. This morning when my supply air coming in was 55 degrees the return was 66 degrees and it was 69 in the house. Now that it's 74 in the house naturally the temps are going to be higher. There is something else I haven't mentioned. The condensor is a 2 stage. It runs on 80% most of the time and only kicks it up to 100% when it is like it has been these past few days. It occurred to me also that 80% of 3 ton is less than 2 1/2 ton. But I digress.

I'll get the temperatures and post them taken within short order of each other probably in the morning.

[coolmist]

I live in Tulsa and I can't see what your problem is. The design indoor temps at 100 outside are typically figured for
75 inside with a 3 degree temperature swing up by the end of the day. Sounds in light of the weather we have had this last few days that your system is doing great. Go by Palmer supply
company in OKC and they sell wet bulb thermometers to anyone if you need one.

[ms7168]

Thanks for that. I appreciate it.

What we are trying to figure out is why I start the day with 50% humidity in my house and end it with 65%.
Quite often that 15% jump comes within a few hours too in the hottest part of the day. Then through the evening and night it comes back down ever so slowly.

I have a feeling it is probably doing as good as can be expected.

[dash]

My guess is :

1.The return ducts leak ,and the return temp.in the house is much lower then at the unit,thus the 10° drop between the two.It might be several degress warmer,with leaking ducts ,at the equipment.This also would pull in warm ,moist(humid) air.

or

2.The fan speed is running on high ,when the system compressor is on 70% capacity.This accounts for the low drop from retun to supply and it also decreases dehumidification greatly.Is the furnace a variable seed indoor fan model?Can yu post the model numbers?

[danj]

Your problem might just be 410 a. It's latent capacity drops off fast at high temps.(much more than r-22) We are seeing a lot of units(puron) that are not able to hold 78 in the afternoons.They climb to 82-83. (It's been 113-116 in the pm) Most 410a units have compressors that are sized a 1/2 ton smaller than the unit rating--- 36000btu compressors in 3 1/2 ton units-- 54000 btu in 5 ton ect. .Reason for this I was told is that at 95 degrees- (in labratory conditions )410a latents capacity is that much better than r-22. Thats where they test the units .There was a good article on 410a and it's preformance verses r-22 on this site a week or so ago. I don't think 410a preforms well in high heat conditions. Just my opion-- I have checked many of these units in the heat of the day and they are doing the best they can do BUT they just can't keep up.
My father worked the numbers(latent capacity) and came up a loss of latent capacity of 18% at 115 veres 9% for r-22 at 115 degrees outdoor ambient.(He's the enginer, not me!!)

[Edited by danj on 07-24-2005 at 12:00 AM]

[ms7168]

Originally posted by dash
My guess is :

2.The fan speed is running on high ,when the system compressor is on 70% capacity.This accounts for the low drop from retun to supply and it also decreases dehumidification greatly.Is the furnace a variable seed indoor fan model?Can yu post the model numbers?

Go back and read the first part of the thread This all began with my noticing I get much better results with a lower fan speed. They told me not to cut it down too low though because we were afraid it might make it freeze up.
If I run it on 1200cfm (3 ton speed) it never dehumidifies well. I can drop that 15% to 1020cfm and that was recommended. I can also use 1000, 800 or 600. I can also either raise those 10% or drop them 10% or drop them 15%.
When I first started the thread I was using 800 plus 10% and believe it or not it was cooling the house every bit as well as it does on 1200 but with a lot lower humidity.

[ms7168]

Originally posted by danj
My father worked the numbers(latent capacity) and came up a loss of latent capacity of 18% at 115 veres 9% for r-22 at 115 degrees outdoor ambient.(He's the enginer, not me!!)

I wondered about that myself because it does slip up on really hot afternoons. The thing I have noticed though is it starts the recovery a lot sooner and gets back to it's target quicker.

[dash]

Originally posted by ms7168

Originally posted by dash
My guess is :

2.The fan speed is running on high ,when the system compressor is on 70% capacity.This accounts for the low drop from retun to supply and it also decreases dehumidification greatly.Is the furnace a variable seed indoor fan model?Can yu post the model numbers?

Go back and read the first part of the thread This all began with my noticing I get much better results with a lower fan speed. They told me not to cut it down too low though because we were afraid it might make it freeze up.
If I run it on 1200cfm (3 ton speed) it never dehumidifies well. I can drop that 15% to 1020cfm and that was recommended. I can also use 1000, 800 or 600. I can also either raise those 10% or drop them 10% or drop them 15%.
When I first started the thread I was using 800 plus 10% and believe it or not it was cooling the house every bit as well as it does on 1200 but with a lot lower humidity.

Okay,assumng your are doing it correctly and everything is working and setup properly so you getting the cfms you expect.

Lowering the cfms ,improves RH,so this supports return duct leak possibility,as less cfms and static in the return,will decrease the leakage(cfms pulled into the return).

Go back and read number 1 in that post.Did you take the temps at inlet and outlet of the equipment,when it's >95° outside.

[Edited by dash on 07-24-2005 at 09:28 AM]

[tinknocker service tech]

return temps 66/68. are your returns low near the floor?
i have seen where low wall returns bringing back cold air affect the txv. cold air as a rule falls and hot air raises and it sounds like you are pulling back all supply.this will make the coil colder and not pull out as much humidity. if this is the case take a three sided box two feet high put in front of the return and see if pulling the air from a higher point makes any differance

[ms7168]

Originally posted by dash
Okay,assumng your are doing it correctly and everything is working and setup properly so you getting the cfms you expect.

Lowering the cfms ,improves RH,so this supports return duct leak possibility,as less cfms and static in the return,will decrease the leakage(cfms pulled into the return).

Go back and read number 1 in that post.Did you take the temps at inlet and outlet of the equipment,when it's >95° outside

Yes I did. That was 64 supply and 74 return.

The furnace is easy to adjust. It has a strip with 12 dip switches on it and the tables with all of the combinations and instructions are in the owners manual. The default combination is for full fan speed for cooling. I have tried just about all of them. The lowest speed is barely a wisp of air. I have noticed the heat using that one on occasion. The furnace picks it's own heat speeds and naturally it tries to use the lowest one it can to do the job. Cooling is adjustable by the user.

It sounds like I should get someone out here to check my return. Even if it wasn't the problem it would at least eliminate the possibility. And it could be the culprit.

[ms7168]

Originally posted by tinknocker service tech
return temps 66/68. are your returns low near the floor?
i have seen where low wall returns bringing back cold air affect the txv. cold air as a rule falls and hot air raises and it sounds like you are pulling back all supply.this will make the coil colder and not pull out as much humidity. if this is the case take a three sided box two feet high put in front of the return and see if pulling the air from a higher point makes any differance

No. This is a downflow system and the return is in the attic and the grille is on the ceiling.