New A/C install- low delta t (cooling)
#1
06-17-16, 12:32 PM
New A/C install- low delta t (cooling)
Ok, Mr cool 3 ton condensor single stage, mr cool 3 ton evap non txv .068 orfice, variable speed furnace set to 1400 cfm final, with ramping profile(not sure static pressure).
Return air is 73.5 Supply air is 60.8 Lower than 15 delta on oversize new unit!!
Home is not efficient at all, old windows and poor insulation and all. 1400 sqft in kc mo(warm and sticky)
How can i achieve a greater split than 13?!?!? Heat index is 100 currently, inside is 74 and climbing at the stat.
Return air is 73.5 Supply air is 60.8 Lower than 15 delta on oversize new unit!!
Home is not efficient at all, old windows and poor insulation and all. 1400 sqft in kc mo(warm and sticky)
How can i achieve a greater split than 13?!?!? Heat index is 100 currently, inside is 74 and climbing at the stat.
Last edited by Houston204; 06-17-16 at 08:20 PM. Reason: Removed charge pressures
#5
06-17-16, 08:23 PM
Forum Topic Moderator
It sounds like you need to lower the CFM to 350 or 400 per ton.
We are not allowed to discuss superheat and subcool on this site.
We are not allowed to discuss superheat and subcool on this site.
#6
06-18-16, 11:23 PM
Dropped to 1100 cfm and split is now 16, but there is very little air coming out of vents. I am aware that i am slightly undercharged. My concern was the pressures. it is 410a system.
You can say "charge" as an issue without directly addressing it. And i will correct it tomorrow. Thanks guys.
You can say "charge" as an issue without directly addressing it. And i will correct it tomorrow. Thanks guys.
#7
06-19-16, 12:04 AM
Forum Topic Moderator
You should have 3 tons of air coming out of your vents.
Are you measuring at return and supply air grills or in the duct just before and after the evaporator coil?
Return air leaks will cause high humidity and a poor delta tee (if the measurements are taken at indoor grills).
In attic installations I usually look for attic insulation that looks like a dirty air filter to point me to return air leaks. Removing the air filter and inspecting for leaks behind it with a flashlight is also an easy check. Duct mastic is not expensive if required.
Supply air duct leaks will result in low airflow from the supply registers and a negative pressure in the house which will pull outside air in from chimneys, kitchen or bathroom vents, around windows and doors.
Are you measuring at return and supply air grills or in the duct just before and after the evaporator coil?
Return air leaks will cause high humidity and a poor delta tee (if the measurements are taken at indoor grills).
In attic installations I usually look for attic insulation that looks like a dirty air filter to point me to return air leaks. Removing the air filter and inspecting for leaks behind it with a flashlight is also an easy check. Duct mastic is not expensive if required.
Supply air duct leaks will result in low airflow from the supply registers and a negative pressure in the house which will pull outside air in from chimneys, kitchen or bathroom vents, around windows and doors.
#8
06-19-16, 07:33 AM
How did you get the measurement of 1100 cfm if very little air coming out of vents ? As mentioned you need to check the leaks. also need to check if the coil and filters are clean. last, your blower motor... These can all affect your air flow and delta-t.
#9
06-20-16, 05:04 PM
variable speed blower has cfm readout on it. I was measuring at living room return and supply registers. It is now 73 in living room(44% humidity)and 79 in hallway(split level home). The air seams to get trapped up there with no where to go. It is 95 currently outside and the charge is correct with a 16 degree split in living room. This unit never shuts off now because IMO there is not enough air movement around the stat. House feels cold down stairs which is an improvement, but now concerned the condenser will never shut off until sundown.
This is a brand new install(new filters, squeeky clean coils.)
No noticeable leaks in supply vents in basement(evap location)
P,S. the airflow reduction of 300cfm dropped my suction side down to 132!
Airflow is my problem i believe not the system itself. Any thoughts?
This is a brand new install(new filters, squeeky clean coils.)
No noticeable leaks in supply vents in basement(evap location)
P,S. the airflow reduction of 300cfm dropped my suction side down to 132!
Airflow is my problem i believe not the system itself. Any thoughts?
#10
06-20-16, 05:07 PM
yes, it is recommended in this area to oversize based on the age of the home and heat load calcs.
we have stretches of 95 to 100+ here. So if you want to keep up in toughs few weeks, we must up our tonnage.
we have stretches of 95 to 100+ here. So if you want to keep up in toughs few weeks, we must up our tonnage.
#11
06-20-16, 09:05 PM
Group Moderator
This is an A/C system..... not a gas furnace converted to A/C ??
By that I mean the registers are high on the walls and the returns are also high or in the ceiling.
I have a split level home with a three ton A/C installed in a gas furnace. Since the ductwork was installed for heat..... the A/C distribution is crappy. The registers and the returns are low. The second floor is always warmer. The downstairs is always cooler.
By that I mean the registers are high on the walls and the returns are also high or in the ceiling.
I have a split level home with a three ton A/C installed in a gas furnace. Since the ductwork was installed for heat..... the A/C distribution is crappy. The registers and the returns are low. The second floor is always warmer. The downstairs is always cooler.
#12
06-20-16, 09:09 PM
If you can keep the house at 73 while outside is 95, and the split is 16. These numbers seems OK to me. Do you really think you have air flow problem ? Can you feel the cold air if you stand 8 feet away from any of the cold air vents ?
#13
06-22-16, 12:38 PM
returns up high, supply are down low.
Maybe i am asking too much out of this unit. Its 98 outside and 77 inside(upstairs stat) 75 mainfloor living. Unit cant produce an even 73 in the heat of the day.
on a side note I am installing new double payn low e and argon filled windows shortly. I am curious to see how much that will help with window radiant heat.
Maybe i am asking too much out of this unit. Its 98 outside and 77 inside(upstairs stat) 75 mainfloor living. Unit cant produce an even 73 in the heat of the day.
on a side note I am installing new double payn low e and argon filled windows shortly. I am curious to see how much that will help with window radiant heat.
#15
06-22-16, 01:24 PM
TADA!! I found that my wife has shut off our other two bedrooms(I never go in these rooms). One bedroom was 85 degrees! this is the same room the stat is touching in the hallway. I am sure by returning airflow to these rooms my split will increase as well as being balanced more. Thanx for all the replies gents!
