Heat Pump Mystery

[wer525]

I'm writing to see if anyone can help solve a mystery regarding Heat Pumps.
I have a two story house with 2, 2-ton Lennox Heat Pumps. I have owned the house for nearly 2 years and have noticed some efficiency problems. I have had the units serviced (no problems) and embarked on some research into why the units run all the time and cost a fortune to operate even with the thermostat set on 79 or 80.

Here's what I found. Some of the research involved multiple units being installed too close together. I measured the distance between mine and it is at about 8". That seemed close to me - so I called a local hvac contractor and was told that 8" shouldn't make a difference in the efficiency of the units. I decided to contact the manufacturer, Lennox to get their thoughts on the matter. I was told by their consumer affairs folks that most definitely having only 8" between the units would negatively effect their efficiency. They said that they recommend 24" between multiple units (and that was substantiated by the fact that it is in the engineering data for the model).

Puzzled, I called another HVAC contractor that I have used in the past (40 years of experience) and he said that "while he wouldn't say separating the units wouldn't help the problem, he didn't think it would solve it entirely". In my discussion with the Lennox rep, he said that being so close together, the units are essentially "competing for air". It is widely known and accepted that you are not supposed to obstruct hvac equipment. So, how could it not be an issue that an entire air intake surface of each unit are 8" apart? Additionally, if they are both running simultaneously, wouldn't they both be trying to draw in air on the obstructed sides and "fighting against each other"
so to speak?

I would greatly appreciate some professional insight into the matter. I understand that hvac contractors and engineers have completely different perspectives - but they can't both be right about this!

[second opinion]

I'm writing to see if anyone can help solve a mystery regarding Heat Pumps.
I have a two story house with 2, 2-ton Lennox Heat Pumps. I have owned the house for nearly 2 years and have noticed some efficiency problems. I have had the units serviced (no problems) and embarked on some research into why the units run all the time and cost a fortune to operate even with the thermostat set on 79 or 80.

Here's what I found. Some of the research involved multiple units being installed too close together. I measured the distance between mine and it is at about 8". That seemed close to me - so I called a local hvac contractor and was told that 8" shouldn't make a difference in the efficiency of the units. I decided to contact the manufacturer, Lennox to get their thoughts on the matter. I was told by their consumer affairs folks that most definitely having only 8" between the units would negatively effect their efficiency. They said that they recommend 24" between multiple units (and that was substantiated by the fact that it is in the engineering data for the model).

Puzzled, I called another HVAC contractor that I have used in the past (40 years of experience) and he said that "while he wouldn't say separating the units wouldn't help the problem, he didn't think it would solve it entirely". In my discussion with the Lennox rep, he said that being so close together, the units are essentially "competing for air". It is widely known and accepted that you are not supposed to obstruct hvac equipment. So, how could it not be an issue that an entire air intake surface of each unit are 8" apart? Additionally, if they are both running simultaneously, wouldn't they both be trying to draw in air on the obstructed sides and "fighting against each other"
so to speak?

I would greatly appreciate some professional insight into the matter. I understand that hvac contractors and engineers have completely different perspectives - but they can't both be right about this!

The hvac contractor has given you bad information, the units need to dissipate the heat that is being absorbed inside of the structure.

[wer525]

Thanks for your response. Forgive my layman's question, but do you mean the units dissipate heat inside the unit itself or by structure do you mean the heat they absorb from the home? If you mean inside the units, the 8" space between them would compromise their ability to to that? Thanks again!

[second opinion]

Thanks for your response. Forgive my layman's question, but do you mean the units dissipate heat inside the unit itself or by structure do you mean the heat they absorb from the home? If you mean inside the units, the 8" space between them would compromise their ability to to that? Thanks again!

In the cooling mode your unit would absorb the heat inside your house and would need to reject it out side. If the units are restricted by being to close to each other or a fence, wall, plants etc. the heat will not be rejected from the refrigerant in the system as it should, and will lead to performance issues and failures.

[John Culpepper]

Picture a heavy set guy running a marathon and all he can breathe through is a soda straw. That is the best analogy I can think of for your situation.

[HVACTechNC]

Based on what you have told us thus far I would agree with the second contractor you spoke to. It is always advisable to install equipment according to manufactures specs. If they say 24", then 24" is the ideal. That being said, two units installed 22" apart probably would be fine... 8" is a bit tight, and the two units are competing for air, but I would not think this is 100% of the problem if they cannot keep up even with the thermostat set to 79 or 80. Before you go moving equipment at a high cost for little efficiency return consider the following:

Find a pro you trust.

Have them check
1. Airflow: Look for obsructions in the supply or return air distribution system. Have the coil cleaned if needed, and have them determine the cfms your system is operating at.
2. Static pressure: Have them perform a esp test to determine the return static, supply static, and then calculate the static of the air handler to determine if the design of the ductwork is restricting airflow
3. Have a superheat/subcooling reading taken to verify proper refrigerant charge and balancing of the system.

I suspect that if those items are done another, more obvious cause will be found, and then a real solution can be proposed either as an independent solution or in concert with moving one or both of the condensers.

[dandyme]

Consumer Affairs ( whomever the mfg is) only knows what they can read.

there are mfg's that do have engineering literature that will permit units to sit as close to each other as 8"

I'd venture you have other issues


Engineering/Technical Representative would have more detail as to the proximity
of units to each other

[timebuilder]

If the units were designed to force hot air out through the sides, then you would have an identifiable problem. A contractor with a flow hood can compare the airflow out the top of one unit when only one is running to the flow when both are running. That will tell you if you need to move a unit.

From a standpoint of aerodynamics, I would expect enough air to be drawn in through the 8" gap to be able to satisfy whatever the flow rate is on a typical fractional horsepower condenser fan motor.

You need to have the system checked. My money is on duct leakage and whether the duct design meets the needs of the rooms it serves.

[Breeze]

From a service stand point a complete walk around would be nice. But you asked about efficiency, what are your KWH per day, per month, should be on your bill. When you say they run all the time, both or one more than other, does your stat tell you run times, are you or someone home all day?
Have them serviced, on a day that ac is actually needed, the tech could check pressures on both units at same time both on then one off. Compare readings.

Since you are only talking one side of unit they both will get about same amount of air but when one shuts down the other could bring in any excess heat from other, which may be bad, a tech should be able to eliminate this as the real problem.

[mlc1955]

definately seperate the units by at least 18 more inches but i would suggest a load be done on the house floor by floor and also check the equipment to find out if they are performing to full efficiency. sounds to like other issues than just to close.

[cuchulain]

We have multiple units that sit this close together all over down here. In our area many of the condensers are on platforms and were built for small inefficient units, and as the units gained efficiency and size the room on the platforms shrunk.

this may hurt the actual functional efficiency of the units but not anything noticeable. You have other issues that should be addressed prior to worrying about the 8" space. Check ductwork, check static pressures, check for cleanliness of the coils. Much as everyone else has said.

[beachtech]

my question is... how does something pass code like that?

anyways. amm certain that the installation instructions have minimum clearences for those units clearly labeled in the first few pages, and should be followed.

is there anything above these units as well? like a deck? lol

as far as having them "maintenanced" well, that's open for interpretation as well... hopefully that maintenance includes chemically cleaning the outdoor coils...

i can see where 8" of seperation would cause high operating pressures, and poor performance. sure wouldn't hurt to meet the manufacturers guidlines IMO

[beshvac]

sorry clicked the wrong one.....

there are alot more factors too. I have a customer that has 2 units side by side, with manufacturer's clearances supported.....But he built two 6 ft privacy fences to hide them on either side (front is open). On a 85 degree day, its about 114 degrees down by the condensers.

[tinknocker service tech]

yes your units are to close and it does have an affect on the. I also agree with you second contractor that moving the unit apart isnt going to resolve you real problem
at best it will help the units effiency but you from what you have said have other concerns going on there
make sure the systems are sized correctly and the ductwork is also sized properly this can also cause the units to not operate properly and run you bill up
before moving them and the expense of it find out the real problem fix it and then move the units

[timebuilder]

sorry clicked the wrong one.....

there are alot more factors too. I have a customer that has 2 units side by side, with manufacturer's clearances supported.....But he built two 6 ft privacy fences to hide them on either side (front is open). On a 85 degree day, its about 114 degrees down by the condensers.

Last summer, a church member told me we were having problems with the AC.

Before choir, I walked around the side and saw the problem. Nine CU's, all enclosed by a privacy fence. Several feet of clearance, but it created a heat island with the fence on one side, and the building enclosing the other three sides.

The fence is gone this year. Bingo, all's well.

[wer525]

I found a copy of the engineering data for my model and it states that there must be 24" between multiple units. I'm getting a lot of mixed input. On my poll, 9 have selected "Yes, multiple units installed too close together does effect their efficiency" and only one selected "no". Hoping to get the contractor who installed them to move one of the units about 4 feet to the left (have to accommodate my crawlspace door). Thanks for your input.

[wer525]

Last summer, a church member told me we were having problems with the AC.

Before choir, I walked around the side and saw the problem. Nine CU's, all enclosed by a privacy fence. Several feet of clearance, but it created a heat island with the fence on one side, and the building enclosing the other three sides.

The fence is gone this year. Bingo, all's well.

timebuilder, thanks for sharing that example. Your scenario seems pretty close to what
I'm dealing with - but I don't have fencing around the units or any major obstructions apart from the units being only 8" apart. Not sure if that alone is enough to effect their performance. I spoke to yet another HVAC contractor today and he suggested getting both units running and feel the air expelled from the top of each one. Then, take a sheet of cardboard and insert it between the units while running and see if I can tell a difference in the temperature of the expelled air.

[timebuilder]

timebuilder, thanks for sharing that example. Your scenario seems pretty close to what
I'm dealing with - but I don't have fencing around the units or any major obstructions apart from the units being only 8" apart. Not sure if that alone is enough to effect their performance. I spoke to yet another HVAC contractor today and he suggested getting both units running and feel the air expelled from the top of each one. Then, take a sheet of cardboard and insert it between the units while running and see if I can tell a difference in the temperature of the expelled air.

Have your contractor measure the "delta T" across the coils. That is also key, because if it is high, the air will tend to spill out the end of the fan blades, which can encourage the air to be drawn back in through the coils for another heating.

High delta T will mean a good coil cleaning is in order.

BUT, I feel you root issues are elsewhere, as already mentioned here by others.

[pacnw]

1st, I did not read all the replies, so if this was said ignore it.

I think your question and the answers are a bit backwards/misleading.


"Do multiple Heat Pumps installed too close together work properly?

Yes - does effect performance and efficiency

No - doesn't effect performance or efficiency"

I think the "YES" and "NO" should be reversed, correct?

[skippedover]

I think you've struck on a valid issue but I also think you're spinning your wheels on a red herring. You need to have a highly qualified tech actually come out to your home and evaluate the system. This tech must know about the effects of airflow on system capacity and he must know how to properly charge a system using superheat and/or subcooling. He must be able to spot a dirty condensing unit as well as a dirty indoor coil, dirty blower wheel and closed or obstructed dampers. If he/she is lacking any of these skills, you're wasting your money to have him visit your home. I hate to admit it but you stand about a 1 in 50 chance at best of finding that individual in your area. I wish you success.