issue with den overheating/underheating

RDSTEAM

i just went to do a HVAC pm on a customers house for the first time. she informed me that the den (which was an addition put on the house about 10-15 years back) doesn't properly cool in the summer and properly heat in the winter. i examined the system and found several issues. this is a forced hot air system with no duct modifications for the ac install. all my supply grills are near the bottom of the wall and several returns located at the bottom as well. I informed them that the cold air is just blowing across the floor and being sucked back into the return almost immediately. thats not the big issue though. the side of the house with the returns is much cooler than the side where the newer den is located. the den has two supply grills at the bottom of the wall but no return at all. the den is somewhat isolated so i feel that there is nowhere for the air to circulate and its somewhat stagnant. i also saw that the humidifier damper was open so i told them to keep that closed during the summer and reopen it during the winter. i closed off a return in the cool damp basement to try and pull a little more return air from the main floor as well. i don't think this is going to help the issue with the den however. i performed a quick load calc while i was there and the system is basically sized on the money. i suggested an attic fan to keep the attic space a little cooler. would it help if i install a transfer fan from the den to the attic and use that as a heat removal method for the summer??

icesailor

Undercooling:

I see that often only it is on heating. Shops with a WA furnace in the rafters with the holes cut in the bottom of the duct work and the fan blowing down with the return in the back. It;s like ME's late energetically challenged Brother In Law. Round and round with no placxe to go.

I suggested and it was done, to run the return ducting to 18: off the floor. Amazingly, it solved the problem on more than one occasion.

RDSTEAM

in winter????

will this effect the ability to warm the home in the winter time?? this furnace is located in the basement. and raising the returns to 18" off the ground is maybe only a foot higher than what it's at now, do you think this would really solve the issue of the den, even without a return in there??

Techman

over/under

What are the dimentions of the den? Is there a basement/crawlspace under the den? What size are the supplies for the den?Are the supply wall registers "one way " blowing the air up towards the ceiling(somewhat) ?The den has to be kinda small with only two wall supplies.If the returns are in the wall ,can the walls be opened and a hi return/supply added? Why not floor supplies?What does a hot air duct system with no modifications for AC mean? With the returns located far away from the den then air flow will be affected . Where is the t'stat located? Put the fan switch in the ON position ,for a week or so,to see if the air/temp stabilizes out a little better.By closing off the basement return I think the overall problem would be worse.How does the return air get from the house to the basement?Putting a transfer fan from the den to the attic will only bring unconditioned air into the house/den. 30 CFM out will bring in 30 CFM of outdoor air.By adding the den and having the AC still sized properly means the AC was oversized in the begining.

RDSTEAM

....

i'll try to answer all the questions asked. den is above crawlspace. insulation is good and had plastic barrier as well. walls are insulated. ac may have been added after addition (addition is roughly 15 years old) owners are somewhat new to home (couple years, alwayshad this problem) no returns in den. one supply register (low on wall) directly behind tv which obviously doesn't help much, one is on the opposite side. i'm thinking the supply air is enough it's just that there is no return in the room. the side that cools well has i believe 3 returns. home began as a hot air system with the addition of cooling. no mods to duct system means all registers located at bottom of wall, returns down low as well.

Techman

over/under

Well,if you are talking about the typical/regular/normal kinda ductwork for heating only-originally- then you might have a ducting problem.And adding a good duct for the den to a not-so-good heating duct system usually doesn't cut it for AC.If everything else is OK,then,can you add a return duct thru the crawlspace? Can you convert the wall supplies into returns and add a couple of floor supplies? Returns are supposed to be bigger than supplies.If the den has a few exposed walls ,that might be a problem.

RDSTEAM

den has

3 exterior exposed walls. it's basically a bump out in the home. i'm thinking maybe i can add a floor return and move the supply registers up higher on the wall and size them properly. i think this will help out enough to not notice the drastic difference in temp throughout the home.

Techman

over/under

If this duct  conversion stuff is going to be "to involved" for the H.O. then maybe a ductless split H.P.?

RDSTEAM

ductless split

is probably their last option. i think they would just rather deal with the temp difference than spend a couple grand for a ductless unit install.

Techman

over

What were the P/T readings from this system? The readings will tell if there is a duct related problem to begin with.

RDSTEAM

p/t

house was warm when i started the system. txv was maintaining about 12-15 degree superheat. approach method was dead on and subcooling was roughly 10-15 as well. pressures were all fine. had roughly a 15-20 degree delta t across the evaporator. everything is fine in the house, it's just the den thats screwy

Techman

under

Just a Q or two.How long are the supplies now? Are the den supplies supplied by flex? 6" ? Regular round metal  6" is only 110CFM . 8" is 225CFM. 400CFM per ton!Kinda Sorta 20-30 BTU per hour per sq. ft.

RDSTEAM

didn't

look into duct sizing very much. i have to go back there anyway so i'll check everyting out