Measuring efficiency of hydronic air handler?

Timco

Chilled water, 4-pipe air handler. 2200cfm. Big sucker, 1960 install.



Unit in question is 3000sq'. Not much air felt from the vents. Coils cleaned thoroughly. 45* water in, 55* water out from AH coil. At the tube, it's also about a 10* delta T. (10 stories, 26 units total)



One competitor wants to record delta T at the AH for a few days. I'm saying the inability to cool the unit down past 77* on a 90* day says more or as much as the 10* DT. I can increase building flow by cutting off bypasses in the attic at the ends of the runs.



The idea is to swap this AH with a new unit, I have specs in an email. What is the best way to measure the improvement from old to new, and what's the rule of thumb for CFM vs DT when figuring out why the bigger upper floor units can't get below 77* when 3rd floor units (west exposure) can get to 70* or lower with the same water temp?

Harvey Ramer

Fan

Clean all the blades on the fan too. Makes a big difference if they were dirty. A squirrel cage fan with forward pitched vanes looses a lot of air flow capacity if the vanes are dirty.



 If you have a tool to measure the actual CFM, do so. If you don't, measure the total external static pressure across the airhandler and compare it to the blower charts. That should get you close.



In order to calculate the output of the coil you will need a psychrometer  and a psychometric chart. You need to plot the difference of enthalpy from return to supply.



Here is the formula to calculate the total output.  BTUH total = CFM x Enthalpy in BTU per pound x 4.5 x (Density ÷ 0.075)



Harvey

icesailor

Fans:

You could be the hero of the day if the problem is the fan blades. I've seen many oil burners with barely enough static air pressure, run like new once I cleaned the inside of the blades. Take a screw driver and run it along the insides. If a lot of lint and dust drop off, clean it. Also, check the face of the blades. If they are irregular and rusted away, they won't make and push as much air. If the fan isn't producing the rated amount of air from when it was new, what are you going to compare it to when you try to pick a new one? It worked before didn't it? I used to service a concrete plant and they had a large oil burner to heat water for cold weather mixes. The burner picked when it was installed was at the end of its range for firing rates. Which determined how much air you could jam down the tube to mix with the fuel. It was always dicey because the Portland Cement dust would stick to the undersides of the fan. I would clean it off a couple of times a year. After a few years, I couldn't get enough air into the burner to get a good burn. I sold them a bigger dual fire burner where the firing rate was close to the bottom of the ability of the burner to mix oil. They have never had another problem.



If the edges of the blades are worn and rough, replace the fan. The roughness will cause turbulence in the air flow and cause the air to "Stall" and cut down on the airflow. If you understand about aircraft, it is similar to an aircraft developing ice on the wing. It disturbs the airflow. It is really important and critical. When you get up on a cold morning and your car is covered in frost, that thin light coating is enough to make an aircraft crash. The turbulence so disrupt the airflow that the wing is unable to establish lift to fly. Also remember that it is only the first 1/2 of a wing that has attached flow. The rest is separated flow. If the flowing air cant attach, it can't fly.

Don't fall into the traps laid by the trial and error mechanics. Change everything until the problem goes away.

If the fan is that old, it needs to replaced anyway.

hot_rod

Did it ever perform properly?

It may have been mis-sized or ducted wrong from day one.



A flow hood would allow you to measure all the discharges and see what the current one is doing at the remote units especially.



Pulleys may have been changed or adjusted and it is not running to spec.



It could be a balancing issue.

Techman

Air handler

Are there "fire dampers" in the ducts? Are the "air cutoff plates" in place in the squirrel cage blower housing? 2200 CFM? That's just over the 2000CFM of a 5t AC system!?What is the blower motor run load amps, compared to the actual running amps? Are there "balancing dampers" in the ducts? What is the return duct system like?

Timco

over my head

Fan blades were cleaned last summer when I did a unit-by-unit cleaning of each AH. Fan and blades were cleaned, as well as the coils. Much better air flow, but not enough to satisfy the 3000sq' units.

Timco

fan age

This is why they plan to just swap them anyway. Age, inefficiency.



If I pull the top cover off the front, massive air. Massive. Inside, not much.



No fire dampers.



A few balancing points in long, straight runs.



Most residents and managers have only experienced recent performance, which is low. Motors have been swapped with 1hp from 3/4, pulleys have been changed, and so on. I can find no other restrictions on the output side.



2200cfm seems like a lot, but there's barely any air coming out the far vents, and not much more closer to the AH. Glad they're swapping these.



The room the AH sits in is part of the return. The return just ends in that room, and you can open shutters to get outside air. Then the AH pulls from that space. In rooms with 2 AHs, if someone burns toast, the other unit gets that. This will be addressed when new AHs are ducted in.

icesailor

Another consideration:

Here's another consideration.

I did work in a bank. The building was built in 1970. Heat only except for the lobby that had AC for the summertime. Dedicated only AC for just that area. Unit was in attic above the lobby/Teller area. Heat was hydronic baseboard with ODR. Worked fine.

1998, complaint was that the building was overheating. After many expansions but no change in HVAC. The problem? In 1970, there were no computer terminals at each teller station and far less humans in the building giving off heat. Solution, run AC in lobby in winter and AC the rest of the building. 15+ VDT's with dedicated hard drives slaved to a master computer in the cellar. Each was probably worth 1500+ watts. Add that to the heating/cooling load.

What is this building being used for that was built in 1960? Have they added mots of heat generating appliances? Like lots of fluorescent lights with transformers?



Its the broken shoe lace that trips you up every time. Its like going duck hunting. You can bring down a flying duck with one bullet from a .22 caliber rifle. Odds are far better with a shotgun and many, many pellets. The odds are just better.

Timco

AH design

Top 3 floors have 2) 2200cfm AHs. (3000sq' each, 2 per floor)

Next 3 floors down have 3)1600cfm AHs. (2000sq' each, 3 per floor)



Then smaller from there.



Top floor is 6000sq' and I have not seen the drawings on what was installed but it's easily twice the biggest units.

Timco

condos

Condos since 1960. No changes. no extra units. No expansions or remodeling. Maybe some minor interior remodel here and there. 

icesailor

Changes:

I'd still be looking for something to be wrong or changed. Someone mentioned fire dampers in the duct work. Are they normally opened when the fire alarm system is operational? Did they change the panel and now they are powered closed? Which might mean that someone had to change switch settings to allow the dampers to be closed and not shut things down.

You might have no idea to the lengths that hackaroos can go to fix their own created problems.

Something changed. Someone did something stupid like changing a drive belt and swapping for a different sized pulley, slowing the fan down. Is it 3 phase in the building and that is a 3 phase motor and it is running backwards because someone switched phases and didn't realize that that was the only 3 phase motor and it's been running like that for over a year. That happened to me. How I learned a long time ago that 3 phase motors run backwards by switching any two feed wires. And they still pump water or blow air in the same direction. Just not as much.



Sometime back, El Cheapo Management may have gone with the $1,000 full service special when they should have gone with the $2,000 comprehensive inspection with the lead "A" team guys. Not the rookies.

Does it use those Honeywell "Modutrol" motors and 3 wire damper motor actuators to run the dampers? If so, those will REALLY make you pull what hair you have left out of your head. Unless you understand how those potentiometer controllers work, you can go nuts. Especially if the attic AH is a heat recovery type and can draw outside air to mix fresh air.

It really sounds like you have a control issue. Not an air handler replacement situation. Does anyone actually know how the whole system is designed to run? If its an air exchanger, you could have an exhaust damper stuck part way open and dumping air to the outside.



Boy, could I ever enjoy rooting around in THAT place. That's what kept me going for a lot of years. A challenge like that.

Harvey Ramer

Vents and Louvers

If you are bringing fresh air into the building, you have to exhaust an equal amount of air to avoid pressurizing the space. Somewhere there should be either a barometric damper or a power exhaust fan. Check to make sure they are working. If they aren't working and you have even slightly leaky louvers in the return air room, you could be pressurizing the space to the point where the airhandler can't move the required volume of air.



It could also be undersized ductwork and undersized equipment. The top story load is always higher and if they used the same rule of thumb as for the rest of the building, they might have missed the mark.



One of the first things I would be doing is measuring air flow and checking the ESP across the air handler. That way you at least know what the equipment is doing.



Harvey 

Techman

air handler

2200cfm for a 3000sq.ft apartment does not sound right, not w/ a 60's construction,not a top floor. How hot does the attic get? KindaSorta , 400cfm =400sq.ft. =1t ;2000cfm=2000sq.ft=5t. A heat loss/gain will tell you how many CFM is needed.

icesailor

Chicago Air Handlers:

Sorry, I just checked and realized that this AH is for cooling. But the same circumstances may still apply. They go either way.



If it is an air handler in Chicago, that does fresh air changes, it has to have a cold air safety on the cold air supply. Actually a By-Pass damper system. The safety keeps the coil from freezing if the incoming air becomes too cold. If it has mechanical by-pass dampers, they can be stuck in a position that cuts down on the flow. Or if it has Modutrol motors to control the dampers, they can hang up open or close but go the opposite way. And turning the potentiometer control doesn't make them open quickly. They are very difficult to troubleshoot until you understand how they work. There will be no "barometric damper" involved.  What kind of air handlers are these? Are they heating only of both heat and AC? The control systems are complex and sometimes field wiring gets changed and not properly followed. What brands are these? How many HP's are the drive motors on the top floor?

Also, the dampers from lack of maintenance, can be frozen in some position from lack of lubrication on the bearings. If they have dampers on either side, the Modutrols work opposite to each other.

And maybe it has nothing to do with your problems.

Timco

Air Handlers

Sorry for the major delay. Got back into that building.



Major leakage in each AH room, and those sit outside the condos. That is being fixed as I type.



Question is, upper floors. They can only make 77˚ with 45˚ water circulating. Lower floors can get 68˚ no problem. Winter heating is fine, but they run 160˚ - 180˚.



1...What advantages do modern AHs and coils have over the older ones? They remove & add more BTUs from the air? Would modern AHs improve the upper floor's performance?



2...What is the math to get needed return grills sq" per 1000 CFM AH? There's just a few small floor registers allowing return air into the floor plenum then back to the AH room.



3...If air can barely be felt coming from the vents (bought hot wire anometer to use Friday) and the motor size & rpm is correct, other than pulley or dirty blades (all cleaned) what would reduce air flow so drastically? Some vents in the units barely feel like air is moving even though this AH is rumbling away. These AHs are huge. 



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