How low can you get SHR in split system?

[pstu]

I am curious what the limits are for getting a low SHR (Sensible Heat Ratio) in a very small conventional split AC system. For something like a 1.5 ton Trane XL14, can you get airflow low enough that it would be effective as a dehumidifier? Or is this a kooky idea?

Was reflecting on the heat output from other dehumidifiers, and vaguely aware that operating costs include not only the pints/kwh Thermastor number, but the added cooling expense from heat output. In the hot-humid climate of Houston TX, some cooling action is needed almost every time dehumidification is needed. In other words, near complete absence of those "cool and wet" weeks that are the ideal conditions for a bit Thermastor.

This may be a dead end idea but I had to wonder.

Thanks -- Pstu

[dan sw fl]

I am curious what the limits are for getting a low SHR (Sensible Heat Ratio) in a very small conventional split AC system. For something like a 1.5 ton Trane XL14, can you get airflow low enough that it would be effective as a dehumidifier? Or is this a kooky idea?

Pstu

One would have to know the SPECS at the Very Low flow range for a specific match-up.

I GUESS without the benefit of this info & review ...
SHR might be limited to ~ 0.63

[dan sw fl]

I am curious what the limits are for getting a low SHR (Sensible Heat Ratio) in a very small conventional split AC system. For something like a 1.5 ton Trane XL14, can you get airflow low enough that it would be effective as a dehumidifier? Or is this a kooky idea?

In the hot-humid climate of Houston TX, some cooling action is needed almost every time dehumidification is needed.

Thanks -- Pstu

Not exactly what you asked
___ but many hints are provided in ...

http://www.airxchange.com/pdf/White_Papers_Reports/SHR%20report/SHR%20Report.pdf

[dan sw fl]

I am curious what the limits are for getting a low SHR (Sensible Heat Ratio) in a very small conventional split AC system. For something like a 1.5 ton Trane XL14, can you get airflow low enough that it would be effective as a dehumidifier? Or is this a kooky idea?

In the hot-humid climate of Houston TX, some cooling action is needed almost every time dehumidification is needed.

This may be a dead end idea but I had to wonder.

Thanks -- Pstu

Basically, it varies and
SHR depends on the climate ...

Houston, TX see page 40

https://www.ideals.uiuc.edu/bitstream/handle/2142/11894/TR151.pdf

[pstu]

Basically, it varies and
SHR depends on the climate ...

Houston, TX see page 40

https://www.ideals.uiuc.edu/bitstream/handle/2142/11894/TR151.pdf

Probably I did not read well enough, could you remind me what "beta" is in those charts on page 40 and following? I always have had trouble with those kind of blackboard equations where symbols are not from the English language. I suspect a form of attention deficit on my part.

I appreciate all the clues so far!

Thanks -- Pstu

[beenthere]

How low of a SHR will depend on ow much moisture is in the air.

Cooling coils are designed to remove more sensible heat then latent. So you will always be lowering temp on mild days. Since your not adding sensible heat back to the house like a WHD does.

[dan sw fl]

Probably I did not read well enough, could you remind me what "beta" is in those charts on page 40 and following? I always have had trouble with those kind of blackboard equations where symbols are not from the English language. I suspect a form of attention deficit on my part.

I appreciate all the clues so far!

Thanks -- Pstu

Beta .. - factor for flow rate and power as uniquely defined on page 8.

[pstu]

For the present let us assume 75F db and 63F wb, that equates to about 52% RH. With residential equipment such as the smallest Trane, what can be done without risking damage in order to push SHR down the most? And has anyone done it or think they could if they wanted to?

Best wishes -- Pstu

[Carnak]

I would say if you drop the blower speed down on standard residential split systems you get it down around 0.7 or so based on typical room condition air 'entering it'

SHR depends greatly on how humid the air entering the coil is. The more humid the entering air is, the lower the SHR.

Sort of like how the dehus 'remove lots of pints' when the air is very humid and then frost up when the air is dry.

[pstu]

Let me take as a starting point, a Trane XB12 with what I think are typical operating conditions: 85F db outdoors, 75F db indoors, 63F wb indoors which translates to 52% RH. That is pretty typical, would you not agree?

Coil is what Trane chose to put at the top of their page: TXC018C4. For a 1.5 ton system, total capacity at 600 CFM is 16.6k btuh and sensible 12.2 for SHR=.73 before any tweaking. How low an airflow do you think a professional could set up? I am sure a different coil would be desirable to maximize humidity removal, would anyone care to comment on the characteristics of that coil?

What I imagine would be the result, is a device that removes a certain amount of water and supplies a certain amount of cold air. I'm trying to understand whether it would be possibly better in my climate, than a device that removes water and supplies heat. I cannot remember the last time when I wanted heat, and at the same time humidity removal -- when overnight lows get below 55F or so, the outside air tends to be dry for us.

Like I said before, this may be a kooky idea and I am trying to learn its weaknesses.

Best wishes -- Pstu

P.S. Searched archives and found Airman1 in 2005 reported...
' American Standard ran a coil test on my 2 stage design and found humidity removal as high as 38% (shr.62) ... even though i have never been a dealer they respected me enough to test the design ... i was suprised and greatful ...'

So it would seem 0.62 might be the lowest number reasonable to expect, unless anyone can tell me otherwise.

[Carnak]

If you are quoting airman, then you have changed the context as the nominal 1.5 ton coil is most likely hooked up to a 2 ton condenser so yes you can get the lower SHRs.

I have put up a graphic on this point several times. it shows a nominal 1.5 ton coil mated with a 1.5 and 2 ton condenser. Airflow is varied from 450, 650 and 750 CFM and you see the capacity and SHR of each scenario for both the 1.5 and 2 ton condenser on the same coil.

Where the example differs from your question is I used an 80/67 entering condition and could therefore squeak by with 450 CFM for 2 tons, as there is more heat content in the air than your 75/63

[pstu]

Somehow I do not recall seeing that graphic, but I will try to locate it. Sounds very informative. The different conditions would give the Trane XB12 example 18.0K btuh total and 12.6 sensible, down to 0.70 SHR without any professional tweaking.

I meant the context to include Airman1 and any other expertise our pros could bear on the problem, including particular coils. So long as it falls within the boundaries of professional practice.

Thanks -- Pstu

[Carnak]

looks like a 2 ton with 450 CFM was balancing out down around SHR = 0.63 or so

the balance was at a 35.5 suction temperature not much cushion against freezing. At a 35 F suction temperature that coil would have an SHR = 0.62

http://hvac-talk.com/vbb/showpost.php?p=3144692&postcount=14

80/67 air going into the coil howver so more heat and moisture to grab

total capacity was down aorund 22,000 Btu/hr with a 2 ton condenser

with higher airflow, the same coil and a 1.5 ton condeser was good for about 19000 btu/hr with SHR probably up around 0.8

to figure out the SHR, you have to see which air flow line you are looking at, see what the suction temperature is and go back and interpolate a little from the data table I put up