I don't think you're out of line at all, and in fact slightly under gives you a little more run time, which is better for removing humidity. And slightly under with less airflow would maximize humidity removal (lower ADP and longer run time).
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I don't think you're out of line at all, and in fact slightly under gives you a little more run time, which is better for removing humidity. And slightly under with less airflow would maximize humidity removal (lower ADP and longer run time).
Gary, I'm going to the jobsite. I've got a couple of men down there right now trimmin' out the cases, and fitting the receiver. I'll get those temps for you.
see, ya.
The Prof suspects if you were to show up at the seminar on time, (and that you advised John Murray that you know the Prof), a spare chair will be found.... :)Quote:
and the Supermarket Seminar in Arlington is <i>BOOKED</i> and there's no space for me!!!!
Quote:
Originally posted by Prof Sporlan
The Prof suspects if you were to show up at the seminar on time, (and that you advised John Murray that you know the Prof), a spare chair will be found.... :)
The Fish suspects that the Prof. advised Mr. Murray, that if there is anyone in the state of Texas, or the international forumn in which he participates, there is no one more in need of the information provided by the seminar! :p
I will likely roll the dice on the Professor's assurance and "crash the party"! :D
Gary, I went out to the site as I said, when I said. When I arrived, the evacuation process was just being completed. The case was at about 46'F - 47'F, so SH readings/adjustment did not commence. The case is full of product, and we decided to let it pull down overnight before fiddlin' with it.
But, the HP was at 210psig
SST at 26'F (49'F case)
Just because I was there, the liquid line temp entering the box from the C.U. was 104'F
Having my meter in the case to check case temp, I measured entering evap temp @ 47'F, air exiting at back wall of case 43'F.
We are anticipating needing to decrease superheat setting tomorrow morning.
I suspect the outdoor temp was 80ish?
Marc, isn't airflow (volume) involved in the equation? Would the "constant air volume" be a variable? i.e.,... a variable as opposed to a constant?Quote:
Originally posted by Fridgetech
...coil capacity is about
kW/mē.K
Where
kW = Capacity potential
mē = total surface area or for a certain coil block the face area
K = LMTD otherwise TD for constant air volume
A variable constant? :confused:
Maybe you could say NO because the reduced volume results in increased TD (LMTD... whatever. I haven't bought the book yet) If that is the case. I haven't really thought about it like that. But the increased TD (lower SST) results in lower C.U. capacity.
Again, I envision the low velocity unit cooler with more coil surface area than an equivalent rated standard velocity unit cooler.
yeah, I think about 77'FQuote:
Originally posted by Gary
I suspect the outdoor temp was 80ish?
Pulling a pretty good load then. I suspect you won't need to adjust the TXV's. The low delta-T means it's sucking up lots of humidity. So far so good. :)
Gary,
Tomorrow I'll fill you in on the final readings. I've never concerned myself with dT, so I'm real interested in your evaluation of those numbers.
Thanx,
Mark
Here's what we know so far:
Normal load is SCT about 20-35F above ambient, 20F being a light load, and 35F being a heavy load.
At 28F over ambient, this condenser is getting rid of a fairly heavy load of heat. Where does that heat load come from? The evaporator.
If the TXV's weren't somewhere in the ballpark, it would not be able to pick up this much load.
The evaporator coil does two things. It cools the air (sensible load) and it de-humidifies the air (latent load). It isn't picking up much sensible load (low dT), so it must be picking up a heavy latent load (lots of humidity).
Make sense?
Quote:
Originally posted by Gary
Normal load is about 20-35F above ambient, 20F being a light load, and 35F being a heavy load.
I don't understand what you mean by "load", light or heavy ... 20-35F above ambient ? what does ambient have to do with load? are you assuming that the ambient is the "infiltration" load? No, by ambient, I am referring to condensing ambient. the case is indoors. typically I assume a constant 80'F for the air conditioner not working properly.
28'F over ambient? Where are you deriving that from?Quote:
At 28F over ambient, this condenser is getting rid of a fairly heavy load of heat. Where does that heat load come from? The evaporator.
...... okay........Quote:
If the TXV's weren't somewhere in the ballpark, it would not be able to pick up this much load.
Agreed.Quote:
The evaporator coil does two things. It cools the air (sensible load) and it de-humidifies the air (latent load). It isn't picking up much sensible load (low dT), so it must be picking up a heavy latent load (lots of humidity).
see above.Quote:
Make sense? [/B]
ohhh! your referring to the condensing temperature above the condensing ambient! right?
Therefore you are determining that the system is doing a great amount of work, and concluding that all is well!!!!
I think I follow you now, please reaffirm.
ADP??????????
SCT??????????
???? SCT = Saturated Condensing Temperature........:cool:
NO?
210psig head pressure = 105F SCT (saturated condensing temp) minus 77F outdoor temp = 28F over outdoor ambient.
see previous posts.... you and I are online simutaneously.
SCT = saturated condensing temp
ADP = apparatus dew point = the dew point of the coil
We are singing a duet :)
Wow!!!
I've never evaluated a system by that criteria.
I like it. (of course when it's good news)
Are there any specifics to account for how much work is being done utilizing the SCT?
there seems to be some amount of frustration on behalf of the forumn, in regard to my reference to TD in addressing design humidity.
but I reference a guide in the Bohn engineering data manual which specifies humidity applications, according to design temperatures, and relates the desired criteria in TD (SST).
I assume that this is my miscommunication with Marc, being that he is intimately familiar with the logistics, however i keep referring to a rule-of-thumb.
Marc could no doubt tell you to the fraction of a BTU :)
And keep in mind that I have made assumptions. Given a full set of numbers, I would be going through several variables before reaching this point in the evaluation.
In regard to the SCT, and your understanding of the design load, typically in My market, we are most comfortable with SCT at or about 120'F (250psig). In august we'll live with up to 270psig without having a cow!! does that change your view on the operation.
Mind you, what makes most sense, and the thought that occured to me when I was looking at the SCT when I was on the roof, was indeed the 110'F SCT compared to the 77'F ambient that I was standing in.
TD refers to a temperature comparison of two different things.
dT refers to a change in temperature of one thing.
What two temps are they comparing in reference to humidity?
TD... believe me... I live by the difference in definition, and I understand it.
You don't think the Prof. would send me to Dallas if his assurance wasn't a sure thing, do you?
Not at all. Being in a very hot climate, you probably have oversized condenser coils. In that case, 28F over ambient is a very heavy load. And as I said, I have made assumptions.Quote:
In regard to the SCT, and your understanding of the design load, typically in My market, we are most comfortable with SCT at or about 120'F (250psig). In august we'll live with up to 270psig without having a cow!! does that change your view on the operation.
Say in the Bohn eng. manual, it would spec (I'm not looking at it now) convenience store cooler app. 70% R.H, 35'f box, TD = 13-15'F.
Have you ever referred to that manual?
So might the Prof, but he is perhaps less incitable than Marc.... :) Maybe not with hvac/r terminology, though :)Quote:
Marc could no doubt tell you to the fraction of a BTU
Well, the coils are only what the mfgr. provides. I base the selection on the mfgr criteria according to max. ambient conditions in which I employ them. Technically, I could spec a very, very undersized condenser coil, however, merely hve a C.U. (compressor) that will provide the required capacity at the given maximum conditions with the condenser coil employed.Quote:
Originally posted by Gary
Not at all. Being in a very hot climate, you probably have oversized condenser coils. In that case, 28F over ambient is a very heavy load
Does that make sense?
They are referring to the difference between SST and evap air in temp.Quote:
Say in the Bohn eng. manual, it would spec (I'm not looking at it now) convenience store cooler app. 70% R.H, 35'f box, TD = 13-15'F.
And as usual only you and Marc would understand it. :)Quote:
So might the Prof, but he is perhaps less incitable than Marc.... Maybe not with hvac/r terminology, though
Don't get me started in the terminology dept.!!!!!!
I think the terminology is the hang-up.
....and someone has brought it up before..... that terminologies may differ (across the "pond") in their daily usage. However when that subject was at hand, I did not feel that was the case, because it was concerning the difference between dT and TD. I am not confused in that regard.
I refer to TD as the difference between design room temp and design SST.Quote:
Originally posted by Gary
[B]
They are referring to the difference between SST and evap air in temp.
If I have a room designed for 35'F space, and a "design" SST of 25'F. My TD is "inherantly" 10'F.
When I say TD, I am referring to design.
I think what you are saying here is that your condensers are oversized for the compressor due to high ambients, compared to the match ups used in cooler areas. :)Quote:
Well, the coils are only what the mfgr. provides. I base the selection on the mfgr criteria according to max. ambient conditions in which I employ them. Technically, I could spec a very, very undersized condenser coil, however, merely hve a C.U. (compressor) that will provide the required capacity at the given maximum conditions with the condenser coil employed.
Does that make sense?
That would be the design TD.Quote:
I refer to TD as the difference between design room temp and design SST.
If I have a room designed for 35'F space, and a "design" SST of 25'F. My TD is "inherantly" 10'F.
When I say TD, I am referring to design.
Once the unit is up and running, you might want to check the actual TD.
As I have said many times, I dont calculate and predict; I measure and analyze. :)
NO, I don't think so. Regardless of the coil area, the compressor must still overcome the lower volumetric efficiency due to the higher condensing temperatures (SCT). So regardless of the coil size, you cannot reduce the SCT. You can only increase the efficiency of the heat transfer, and perhaps increase the subcooling. But the threshold SCT is what determines what amount of power (less loss of compression ratio, thereof) is required.
...perhaps
I calculate and employ.Quote:
Originally posted by Gary
, I dont calculate and predict; I measure and analyze. :)
I do very well........ I think. My track record speaks .....
Quote:
Originally posted by Gary
That would be the design TD.
10-ROGER-A-1-04 :)
That's what I mean.
Try filling a condenser halfway up with liquid. You are in effect reducing the surface area. What happens to the SCT?Quote:
NO, I don't think so. Regardless of the coil area, the compressor must still overcome the lower compression ratios due to the higher condensing temperatures (SCT). So regardless of the coil size, you cannot reduce the SCT. You can only increase the efficiency of the heat transfer, and perhaps increase the subcooling. But the threshold SCT is what determines what amount of power (less loss of compression ratio, thereof) is required.
Okay, I follow you.
SCT is NOT ambient.
But I think my comment regarding the high ambients holds in that regard, because you do not want to empty it.
I follow your point regarding the function of flooded condenser valves.
I don't doubt it :)Quote:
I calculate and employ.
I do very well........ I think. My track record speaks .....
There is nothing wrong with calculating and predicting. This is necessary for designing and sizing systems. But I don't do either.
I am a service tech. The system is already designed and sized. My job is to trouble shoot and repair it. In order to trouble shoot it, I must measure and analyze, not calculate and predict.
It's kinda like reverse engineering. :)
boy...... the messes you must get stuck with.
Hey, your Pm mailbox is full. I tried to PM you.
I think my boss searches high and low for nightmare scenarios to dump in my lap. LOLQuote:
boy...... the messes you must get stuck with.
Hey, your Pm mailbox is full. I tried to PM you.
My PM box says empty. :(