Variable speed air handler settings

ChrisJ

@Harvey Ramer

The air handler I've been considering is American Standard's TAM7. It appears to have a dehumification setting which would be controlled by an appropriate thermostat, but they don't go into detail on how it works. Best I can tell, it would lower the blower speed as you said, and it appears to do so separately from the cfm per ton setting. Not sure what this means if you enable it, and run the lowest cfm per ton setting as well. Does it go lower, or is it bottomed out to begin with?

Harvey Ramer

I can't say for sure what that unit does, as I am not trained by that manufacturer. It would probably be fairly easy to find out if you can get your hands on the engineering manual. Your contractor should be able to provide that.

I know Johnson Controls will run at 50% blower speed for the first 5-10 minutes when set on the humid profile. That is below 350 cfm per ton which is considered the lowest setting for AC.

Harvey Ramer

The other thing you can do if you get their communicating control is manually change the cfm per ton as the seasons change.

ChrisJ

@Harvey Ramer


Here's the two changes we did last night just to see what came up. Keep in mind, the original one I posted before, didn't include ceiling load in one room so that one should be higher than it was.

Gordy

ChrisJ said:

Hatterasguy said:

That would be a DT of 57F in the winter (6F design) and 15F in the summer (90F design), sonny.

And, Gordy is right. You have no clue how high your electric bill is going to get if you run 25F all summer with the 3 ton unit.

Here, I'll do it for you:

4KW for 720 hours in July with an estimated duty cycle of 65%.

1872 KWH @ $0.15 = $280.

Just wait until your wife sees that bill.

6F design?
The record low for my area is -19F.
I've already seen -9F and we had several nights of -5F in 2014. A design temp of 6F may be the case, but I wouldn't go for it, not in my house.


I'm aiming for a 25 degree DT, which is why I put it.

As far as electric bill, I'm currently running 2.5 tons of window units all of which have EER's of 9.2 and they run continuously very often in July and August. I also have a 50 pint dehumidifier running non-stop.


The meme is accurate.

As a goal You should be looking at your present equipment comfort, and operating costs. Then use that bench mark to reduce operating costs, and increase comfort with your new system.

Harvey Ramer

The top one is irrelevant because it's not calculated at your desired indoor temp and therefore does not give you an accurate latent load number. Remember RH is just that. A measurement of moisture in the air relative to the air temperature.

The bottom one is starting to look better but it's still only showing a .85 SHR. I would target 45% RH @70 degrees and run the numbers again.

It's pretty clear that it will require a 3 ton system based on your load. Which is utterly astounding for 1600 sf. But that's why we do the numbers right. The only thing left is to nail your indoor temp and humidity levels and then select the corresponding coil.

If your SHR is indeed acruate at .85, I would consider either jumping a half ton in size on the indoor coil or doing a direct match and running closer to 425 cfm per ton.

The engineering data on the coils should show you the SHR of that coil at various cfm's and various return air Temps. That is the info you need to both set the cfm and select the coil.

Harvey Ramer

A chart like this is what you use to select the proper coil and cfm.

Techman

ChrisJ, I appreciate you wanting your house COLD. Good for you. But the Sensible/Latent ratios are different when its a 80* ambient. So you want 55*F indoor temp? Two stage sounds interesting.

ChrisJ

Techman said:

ChrisJ, I appreciate you wanting your house COLD. Good for you. But the Sensible/Latent ratios are different when its a 80* ambient. So you want 55*F indoor temp? Two stage sounds interesting.

You have a point, except for I don't see anyone that maintains a 75°F setpoint when it's hot out running a 60°F indoor temp when it's more mild out?

Also, using the "old school" 1 ton per 400 square feet, I'd use a 4 ton system.

I don't think 3 ton is unreasonable for my house or my expectations of the system. To be honest, duct losses in the hot attic do concern me some.

For the added cost of a 2 stage unit I'd rather a dedicated whole house dehumidifier.

Techman

Anybody know about the Rheem Inverter unit?

ChrisJ

Techman said:

Anybody know about the Rheem Inverter unit?

I don't.
I'm interested though?

njtommy

At this point in time I Think almost everyone makes an inverter style system for those 20-24 seer ratings.

ChrisJ

njtommy said:

At this point in time I Think almost everyone makes an inverter style system for those 20-24 seer ratings.

They all seem to be extremely pricey as well.

JUGHNE

FWIW, I spoke to the local Lennox man, older guy who likes to keep things simple. He said the early Lennox 2 stage AC were a real PIA. He was very glad when replacement parts were no long available and those units had to be replaced.
The new ones have been good to him. He said the 3 ton steps down to 2 ton as needed. Don't know if anything smaller is available.

Techman

ChrisJ, while you are doing the math and figuring and thinking and stuff ,think about this; I don't know of very many ACR unit where the "heat of rejection", is not, 20-25% MORE than the "heat of pickup". Evap is 12k btu and cond coil is 15k btu.Or put another way, where is the whole house dehumidifier's "evap coil" vs the where is the WHD"cond coil" located?

ChrisJ

Techman said:

ChrisJ, while you are doing the math and figuring and thinking and stuff ,think about this; I don't know of very many ACR unit where the "heat of rejection", is not, 20-25% MORE than the "heat of pickup". Evap is 12k btu and cond coil is 15k btu.Or put another way, where is the whole house dehumidifier's "evap coil" vs the where is the WHD"cond coil" located?

Whole house dehumidifier is one unit, they don't have separate coils. First you pull the air through the evap section and wring the moisture out, then you run it through the condenser and warm it up. There's absolutely quite a bit of heat added during the process.

My basement is 80+F all summer because of a dehumidifier, but I'd rather it hot and dry down there than cool and 80%RH.

Techman

Yea but, you are not cooling off the basement ,so that "extra"btu of rejection stays in the basement. Now,with the new way you WILL BE cooling off the cond coil of the WHD w/ the WHAC (WholeHouseAC)

ChrisJ

Techman said:

Yea but, you are not cooling off the basement ,so that "extra"btu of rejection stays in the basement. Now,with the new way you WILL BE cooling off the cond coil of the WHD w/ the WHAC (WholeHouseAC)

Correct.
The system will use energy to get rid of excess moisture at cooler temperatures.

However, such a system could also be set up to bring in fresh air from outside on cooler nights and dehumidify it as well.

Many options.

njtommy

Yes too many options in my opinion. I fully believe as we move towards the future we will most likely all have inverter technology in our homes of some sort.

Simple is sometimes best, but not always the most comfortable.

ratio

I just started two Lennox RTUs with a VFD driving the compressor. The Prodigy M3 controller runs it & the ECM blower. Pretty fancy.

njtommy

@ratio sounds like a really nice set up. Are they using EXVs or standard in txvs.

ratio

Standard TXVs, I believe. I didn't get a chance to give them a real working over, I had to get them started for temp cooling, & it was late already. My poor sidekick didn't know what to do with them, the M3 wouldn't do anything until you went through its commissioning procedure. A good idea, but I do wish they had mentioned that in the startup docs.

TonyS

Hi Chris, I use the chart as a rough guide and check my duct with a hot wire anemometer I usually will use a Pro T755H stat with humidity control wired directly to the dehum terminal or if using a model without a dehum terminal I will wire in a single pole/double throw relay to a lower fan speed when energized. This makes for good dehumidification without lowering the seer in normal mode.

ChrisJ

TonyS said:

Hi Chris, I

Speechless eh?

ChrisJ

TonyS said:

Hi Chris, I use the chart as a rough guide and check my duct with a hot wire anemometer I usually will use a Pro T755H stat with humidity control wired directly to the dehum terminal or if using a model without a dehum terminal I will wire in a single pole/double throw relay to a lower fan speed when energized. This makes for good dehumidification without lowering the seer in normal mode.

Hi @TonyS
Are you familiar with the Trane / American Standard TAM7 series air handler? That's what I've been considering, and it does have a dehumidify connection for a thermostat. They say it lowers the fan speed, but that's about all it says.

ratio

@TonyS, ever use a stat with humidity control, like the Honeywell TH8321 or Carrier Edge Pro? I like the T775 series, but they seem more like industrial controls that homeowners would shy away from.

ratio

Ah, I just looked at that number again, I be t you're not talking about one of these, are you?

GW

I didn't read every post, just skimmed at a brisk pace, so forgive me if this is redundant.

Generally speaking, in my experience, when you see a static pressure/ cfm chart it's not a variable speed blower, it's a basic ECM, aka X motor.

X motors don't ramp up and down. Variable Speed motors do. Variable speed motors are smarter, you can set the cfm you want. If the duct system isn't too junky you will get the specified cfm

X motor, if you don't check your TESP you have no idea what the cfm is, you're just guessing.

Now if you like the splits you have, no one is going to arrest you for not checking the static pressure aka total external static pressure TESP.

Ac cfm, I believe this has been thoroughly discussed but 400 is average 350 is better dehumidification 450 is better sensible.

If you have a lame-duct system you may need to wind down at 350 just to keep the motor from overworking. Conversely if your duct system is a bit large you may want to crank up the 4:50 just to keep things rolling along.

Retrofit: The Heat gain is one topic, how much CFM the duct system can handle is another one. Hopefully the duct system can accommodate the tonnage you're trying to blow.

Gary

ChrisJ

GW said:

I didn't read every post, just skimmed at a brisk pace, so forgive me if this is redundant.



Generally speaking, in my experience, when you see a static pressure/ cfm chart it's not a variable speed blower, it's a basic ECM, aka X motor.



X motors don't ramp up and down. Variable Speed motors do. Variable speed motors are smarter, you can set the cfm you want. If the duct system isn't too junky you will get the specified cfm



X motor, if you don't check your TESP you have no idea what the cfm is, you're just guessing.



Now if you like the splits you have, no one is going to arrest you for not checking the static pressure aka total external static pressure TESP.



Ac cfm, I believe this has been thoroughly discussed but 400 is average 350 is better dehumidification 450 is better sensible.



If you have a lame-duct system you may need to wind down at 350 just to keep the motor from overworking. Conversely if your duct system is a bit large you may want to crank up the 4:50 just to keep things rolling along.



Retrofit: The Heat gain is one topic, how much CFM the duct system can handle is another one. Hopefully the duct system can accommodate the tonnage you're trying to blow.



Gary

Hi @GW
The AH has two options, constant torque and constant CFM.
It allows you to choose 350, 370, 390 and 410 cfm per ton.

After reading what you said, is this the reason there arn't multiple coil options giving different SHR? Because you just adjust your CFM rating to accommodate your needs?


It's another beautiful day out today. Just jumped up to 88F as I'm posting this. /Sarcasm.

ChrisJ

Current conditions in the middle of the first floor. Part of this is due to not enough cooling power, and another part is due to being too far from the unit. This isn't bad, but it will continue to climb as we get towards the evening.

All 2.5 tons worth of window rattlers are going continuously and have been since this morning.

GW

I'm sorry I'm not familiar with that system. I am only familiar with basic ECM and basic variable speed.

SHR, now you're talking, what are you trying to dial in? Are you oversized, or undersized and wonder if your sensible is adequate ?

Gary

ChrisJ

GW said:

I'm sorry I'm not familiar with that system. I am only familiar with basic ECM and basic variable speed.



SHR, now you're talking, what are you trying to dial in? Are you oversized, or undersized and wonder if your sensible is adequate ?



Gary

@GW
I'm not anything yet, this is a system I'm planning for the near future. According to most, I will be slightly oversized so I'm just looking at my options. Did we the manual J with 95F outdoor and 70F indoor and it suggests slightly larger than 3 ton for those conditions so I'm planning a 3 ton setup.

It sounds like the variable speed air handler will help quite a bit with humidity concerns on cooler days.

TonyS

Hi Chris, not really sure where the reply button is. lol Not familiar with that particular unit. I usually install ArcoAire but they are similar.What I have found out is all ECMs are variable but only upper end ECMs offer the dehum terminal. If your unit has it...use it. It saves you the cost of running a relay. OK now about the thermostats. Not all Honeywell stats that have humidity control have a dehum terminal!! Honeywell simply uses a program that allows the unit to run a couple of degrees below setpoint without it showing on the screen. You can not use this with your ecm dehum terminal because there is no terminal. I use the Prostat I mentioned and sometimes the White Rodgers stat w/humidity. Both of these actually offer a dehum terminal which is energized/ deenergized on call for dehumidification. They also have a hum terminal to operate a humidifier. When the dehum terminal is energized the fan will run at the normal speed. When humidity gets too high the stat will deenergize this terminal bringing airflow back 15 to 25 %. http://www.emersonclimate.com/Documents/White-Rodgers/instruction_sheets/0037-7313.pdf page 4 shows a simple way to change speeds in a non ECM blower. Also Chris I just want to restate the ease of use a hot wire anemometer offers. These units have come down significantly in cost..you simply input the size duct you are putting it into and it will give you a direct readout of CFM. You can use it on branches and trunks,round or rectangular. It simply makes all that figuring go away. These units are highly accurate using the same tech as air mass sensors for fuel injection.

TonyS

Ratio....https://www.pro1iaq.com/humidity-control/t755h

ChrisJ

Still hanging in there with curtains closed and a cloudy day, but everything has been running non-stop all day.

Both floors are slightly warm for my tastes and if you add any extra load from people, or door opening forget it.

2.5 tons cuts it, barely. 3 is a better fit especially if it's sunny out.






The small numbers are the lows and highs since midnight last night.

SWEI

2:15 PM today:

ChrisJ

Where are you located @SWEI ?

SWEI

Silver City, NM
6,000 ft, but ~32° N. latitude

Gordy

ChrisJ

Well,

I'm glad I've proved my 3 ton point finally, @Gordy