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-   -   Central Air Conditioning running all day (http://www.diychatroom.com/f17/central-air-conditioning-running-all-day-98143/)

quaildog 03-12-2011 03:08 PM

Central Air Conditioning running all day
 
I'm writing to see if someone can answer my questions regarding
central air-conditioning or refer me to someone who can. Our new central air conditioner runs all day and the company that installed it says that it's normal.

We live in a 14-year old R-2000 certified home in the country. The house is approx. 1,500 sq. ft per floor and there are a number of large argon-filled windows. After getting a number of quotes,
we chose Sears to install a 2-ton, 14.5 SEER unit in June 2010. Once we started using the unit, we noticed that it was running all day. I started keeping notes and found that it would typically
start around 9:30 in the morning and run all day if the temperature outside was anywhere above 27 degrees Celcius. The thermostat was set to 22 degrees Celcius. The company salesman came and measured the house to ensure we had the right size unit and he had their service people check the system out as well. Finally, the company service manager spoke to the manufacturer who replied that these new types of air conditioners focus more on the humidity and will typically run all day. The temperature in the house might even go up slightly in the afternoon depending on how
high the temperature gets outside. (I had central air in a previous house 20 years ago and if I turned on the AC when I got home from work, the house was cool within a few hours at most.)
The service manager told me that I wouldn't be able to get an AC to operate the way I wanted. Getting a larger unit wasn't recommended either because the fan and ducts might not be able to handle it and the AC coil in the furnace might freeze up completely.

My question is this - is it now typical for today's new AC units to run 10-12 hours a day without stopping or am I being fed a pile of baloney?

My basement ducts are already all closed. Is there anything else I can do?

I find it hard to believe that the AC must run all day, even when the temperature is below 30 degrees Celcius!

yuri 03-12-2011 03:42 PM

1 Attachment(s)
Pure balogna. Probably neither the tech or the service manager know how to properly adjust the freon level and check the unit properly. Probably is low on freon and may have a freon leak. It will damage the compressor from being low on freon so you need to get it fixed ASAP. Your house is the same as mine in size and better insulated and my 2 ton unit runs 20 mins ON/40 mins OFF in 30 deg C weather. Big box stores and S***s use sub contractors and the lowest bidder gets the jobs. I work for the highest bidder who pays the highest wages if you get my meaning. May have to get another reputable co to check it and make a report. Then contact Sears if it does not get resolved then the BBB and then Sears. Finally go after the manufacturer if necessary. They don't want their products to get a bad reputation. The service manager is lying when he said the manufacturer told him that. That is a blanket statement for hot humid climates like Florida where the units run longer to remove humidity. We also downsize some of them too run longer and remove more humidity ONLY if they were oversized in the first place. For a few bucks you can do your own heat load calculation and verify you have the right sized unit. Then they cannot argue with you over the sizing.
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Doc Holliday 03-12-2011 05:47 PM

BS. Units are specifically designed to cycle on and off, dehumidifaction included. Never are they to run continuously, not even if set on low speed during cooling for dehumidification when in fact on variable speeds they can be set to "ramp up" in speed from a low speed for some variable amount of minutes for dehumidification to full speed after dehumidification and then shut off when desired set point is reached and repeat, called cycling. Again, on and off and on and off, never always on as that in itself defeats energy efficiency.

Is this only the condensing unit you had replaced or are we talking the entire system meaning air handler (with evaporator coil in it) and condenser or furnace and individual coil and condenser and what was your old system size?

If you have any of the old system's model and/or serial numbers it would help.

hvactech126 03-12-2011 05:50 PM

it sounds undersized or undercharged, but there are questions we need answered as in the last post. Was a heat load calculation done?

DIY_HVAC 03-12-2011 08:41 PM

The system may be a bit small but that is usually a good thing. A few questions.

Dose it keep the house comfortable?
What was the outside temp?
22 seem a bit low for me. I keep mine at 78 or 25 in the middle of the day and this is quite comfortable.
What is the temperature of the air coming out of the vents and what is the temp going into the return?
Finally was your electric usage higher than expected?

heatycooly 03-12-2011 08:58 PM

For your sizehome you need at least a 2.5 ton probably a 3 ton it is undersized the freon levels are probably right but if its too small it won't shut off

beenthere 03-12-2011 09:38 PM

New units tend to do a poorer job of dehumidifying. So who ever said the manufacturer said that, fed you a line. It sounds under sized.

On a design day, the A/C should run continuous. Do you know what your outdoor design temp is?

AllanJ 03-13-2011 08:22 AM

If you manually turn it off (raise the thermostat temperature setting) every hour for a half hour, does the house not get cool enough?

If the system runs almost continuously on a slightly hotter than normal day and does not cool the house enough on a quite hot day then the system is undersized or needs service (Freon, etc.).
Quote:

Originally Posted by beenthere
New units tend to do a poorer job of dehumidifying.

The system has to be designed to get the proper range of air temperatures at the coil outlet. Generally, the lower that temperature, the better the dehumidification achieved. But if the air temperature at coil inlet together with the volume if air passed are both too low than the coil freezes up. A less sophisticated system may not control the air flow that precisely usig varialbe blower speed, etc. To make up for that and prefvent freeze ups the outlet air temperature is allowed to average higher. Then the system has to run longer for dehumidification's sake. It still stops at the target temperature leaving the humidity a little higher than a better system does for that temperature. The occupants then set the thermostat a little lower and, provided the system is able, everyone is happy.

beenthere 03-13-2011 09:33 AM

Quote:

Originally Posted by AllanJ (Post 608258)
If you manually turn it off (raise the thermostat temperature setting) every hour for a half hour, does the house not get cool enough?

If the system runs almost continuously on a slightly hotter than normal day and does not cool the house enough on a quite hot day then the system is undersized or needs service (Freon, etc.).

The system has to be designed to get the proper range of air temperatures at the coil outlet. Generally, the lower that temperature, the better the dehumidification achieved. But if the air temperature at coil inlet together with the volume if air passed are both too low than the coil freezes up. A less sophisticated system may not control the air flow that precisely usig varialbe blower speed, etc. To make up for that and prefvent freeze ups the outlet air temperature is allowed to average higher. Then the system has to run longer for dehumidification's sake. It still stops at the target temperature leaving the humidity a little higher than a better system does for that temperature. The occupants then set the thermostat a little lower and, provided the system is able, everyone is happy.


Newer systems tend to use a larger indoor coil that doesn't get as cold as older systems did. While you can slow the blower, down, that tends to reduce the system efficiency so that the customer doesn't get the efficiency that they paid for.

Doc Holliday 03-13-2011 11:19 AM

I'd like to know what this system's target superheat was/is and what the actual super heat is. Bets as to it also being undercharged so the sh is higher than target meaning past saturation still being in the evap coil lines and beginning to pick up heat in vapor while inside coil?

Correct to slightly overcharged would mean lower sh but more capacity (of coil, ability to absorb heat from space), txv.

Doc Holliday 03-13-2011 11:29 AM

Quote:

Originally Posted by heatycooly (Post 608073)
For your sizehome you need at least a 2.5 ton probably a 3 ton it is undersized the freon levels are probably right but if its too small it won't shut off


Can you please explain how you came to this conclusion?

Marty S. 03-13-2011 12:11 PM

Could be several reasons why it runs all the time when the temp is above 80 and none of them are normal.

yuri 03-13-2011 12:33 PM

Guys, he has a R2000 home with 8 inch thick R-26 walls and low e-argon windows and perfectly glued sealed airtight vapor barrier. Also has over R40 in the attic. Google R-2000 homes for more info. It is INCREDIBLY airtight and energy efficient. They do a blower door test before certifying it. I saw a 18000 sq ft R2000 home here being heated by a 60% efficient 90,000 BTU furnace. Normal home would have had 135-150,000 BTUs. 2 tons is the right size but it is obviously not setup properly. Plus he lives in a rural area with better breezes and less heat load than being crammed in the city. Probably has good shade trees also.

http://oee.nrcan.gc.ca/residential/p...d/standard.cfm

Doc Holliday 03-13-2011 12:42 PM

Quote:

Originally Posted by yuri (Post 608383)
Guys, he has a R2000 home with 8 inch thick walls and low e-argon windows and perfectly glued sealed airtight vapor barrier. Google R-2000 homes for more info. It is INCREDIBLY airtight and energy efficient. They do a blower door test before certifying it. I saw a 18000 sq ft R2000 home here being heated by a 60% efficient 90,000 BTU furnace. Normal home would have had 135-150,000 BTUs. 2 tons is the right size but it is obviously not setup properly. Plus he lives in a rural area with better breezes and less heat load than being crammed in the city. Probably has good shade trees also.

http://oee.nrcan.gc.ca/residential/p...d/standard.cfm


Hence superheat.

yuri 03-13-2011 12:44 PM

I am sure it is not setup properly. He had a older 10 SEER unit and they did not adjust the fan speeds and superheat etc with the new unit. I would like to know if he bought a new furnace with it. Obviously he appreciates quality and has a few $$ to spend if he paid $10-20,000 more for a R2000 house. If it is a new furnace with variable speed drive they probably left it going full blast for 5 tons of cooling capacity with the fan. Happens all the time.


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