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Can anyone point me in the direction of a free excel or online calculator to measure cooling capacity? I'm looking to measure cooling capacity with blower CFM and temperatures, supply and return as wb and db for inputs. I know I can work this out by hand, but I found a program online a year or two ago that did the work for you.
Have a look here on Prof Sporlans website
http://users.isp.com//aschoen/
Thanks for the link Frank. That gets me close. There was another program that one just keyed in the parameters and gave the cooling capacity.
Working with this program you provide the link for, I can figure out the weight of the air moved from the return in an hour, and from the wb/db know the energy contained in that return air. I can also use this program to learn the energy that remains in the supply air and work out the difference.
Except.... I'm left with a question. Is the weight of the return air (per unit time) identical to the weight of the supply air? If water is removed as condensate, the air will contain less water, be denser since it is cold and be nearly saturated with moisture, all at once.
If I want to learn how much is sensible heat removal, how much is latent heat removal, how do I make these calculations? I can make blower measurements by measuring heat strip rise, but I don't own the instruments to know with precision what air flow is at supply and return sides of the coil. Are there any means of backing into the calculations without measuring air flow both in supply an return. I know air flow for the blower from measuring temperature rise for a known input KW of electric heat. But there is not a latent heat change in that measurement. Is this important here?
Larry, check this software!
Not free: www.handsdownsoftware.com
For STEADY flow and if there are no air flow "losses" and you only take moisture from theQuote:
Originally Posted by Larry2
air, mass conservation holds: Supply Air Mass Per unit time = Return Air Mass Per unit time
+ Condensate mass per unit time.
If still in steady state and incompressible flow (speeds far less than the speed of sound,
and not high pressure losses, no mist, no wave-like phenomena, etc) the mass of the air flow
is equal to the density of dry air times the volme of air per unit time plus the weight of
water content.
You can estimate air volume using an air velocity meter. Air volume=face area* average speed
in that area. If you want to know how it should be done visit http://www.eurovent-association.eu/w.../documents.asp and read Eurovent 5/3 and 5/4 but others are also useful.
Very simple you have to know the dry and wet bulb conditions of the initial and final statesQuote:
Originally Posted by Larry2
(the process path).
The total heat is the enthalpy difference between the two points. The sensible heat is the
enthalpy difference of a horizontal proyection of the process path. The latent heat is the
enthalpy difference of the vertical proyection of the state path in a psychrometric chart. See the right angle triangle here?
It is not difficult to make your own instruments but you need to calibrate them.Quote:
Originally Posted by Larry2
Yes and no. You can measure what goes on in the coil but you have to estimate with this information the air part. Unless you know information not usualy available like the coils (heat exchanger's) efficiency.Quote:
Originally Posted by Larry2
What? If you knew this by measuring only kw input, I've been loosing my time the last 26 years!Quote:
Originally Posted by Larry2
Another way to estimate air flow is with the blower manufacturer's curves, if you have them but you usually need to measure pressure drop of air through the blower. Not kw.
Power input will tell you little of the air flow unless you know the motor/blower's efficiency. At least you'd know the usefull power, all the rest is lost in heat, noise, vibration maily.
Yes. Get psychrometric literature, it is all over the web.Quote:
Originally Posted by Larry2
Hi GXMQuote:
Originally Posted by GXMPLX
Larry is talking about the Kw input to a resistance heater not to the fan.
As in Q = mcdt
Ok Now I understand! ... the correct name is GXMPLX Please! :)Quote:
Originally Posted by frank
Yes you can calculate air flow this way, provided that flow is steady, incompressible and the pressure drop caused by the heating not significant.
No problem if there is no latent heat. This only means that your process with the resistance is horizontal in the psychrometric chart.
You can calculate flow using this process to estimate the air flow but don't think it is better than other methods. It has several sources of error like not heating all the air, only if presure drop is relatively small you can use the enthalpy difference as equal to heat otherwise you have to measure the work done by the flow against that pressure drop too.
If you can estimate the air flow this way, you also need dry and wet bulb (or relative humidity or absolute water content) of both inlet and outlet conditions and will be able to calculate latent + sensible heats of the original process, drawing a line in the psychrometric chart and measuring the horizontal and vertical projections in the direction of equal enthalpy lines.
I suppose you have literature on this.
Thanks so much Nike123 for the link to that application. That is a nice application that will be helpful. It will get me thinking in the MKS unit system too, lol. :rolleyes: It will just take some double checking of my input numbers.
GXMPLX, thanks for your comprehensive answers, some of which will require my further attention without benefit of a cool lager on the desk. . I don't know what I was thinking. For all the air going in the return, the same amount comes out, minus a tiny amount, maybe a pint per hour of water removed. That's probably lost in the measurement error for what I am doing.
As Frank mentioned, earlier I measured air flow by running a known amount of electric heat and measuring delta T to arrive at CFM. I've improved air flow since that measurement. The fan was at stall (starved on the return side) when I started and now it's running around 0.22 WG differential. I need to repeat my work. It was not a fast measurement to make during winter with only one thermocouple. With it 80-90 F summer time heat, it could get tedious. I also got to thinking about air flow with the coil dry during the heat strip measurements vs measurements with the coil wet for my cooling capacity measurements. I could probably gain another 0.1 WG pressure for a wet coil, so I could skew my calculations by making unsupported assumptions. Too many assumptions, I may as well wander around with a damp finger in the air.
I looked into cheap ways of measuring air flow. I understand the principle of measuring velocity in a known duct cross section. I even have a hole drilled in a well suited spot. I'm not quite sure how to do this cheaply and accurately. My wife is growing weary of the growing collection of new/old tools arriving for this project. I point to the cowboy estimates to patch things up and that settles her concerns for a while. We commissioned the new first floor system tonight, and she is all smiles. She can now read the torr gauge and relay the readings over the radio and I know if she means 5 torr or 0.5 torr. Anyway, so for this one measurement, I am looking for a means of measuring cooling capacity with good accuracy, and without buying more <expensive> tools (toys).
I own a very accurate Fluke thermocouple meter, a Fluke 8050A DVM, ammeter, o'scope and lots of bits and pieces to build stuff. I have two magnehelix gauges, (0-1 and 0-1/4) but without a quality pitot tube, I don't think they will help me much. I think the fan table for the air handler is out the window. The blower cage is old, has some surface rust and dirt that would alter the performance. The tables don't match earlier pressure/cfm measurements.
My goal is to learn what my cooling capacity actually is so that I know if I should change the size of the replacement unit. This is the 3-1/2 ton 1991 unit that old readers will recall I installed a 4 ton compressor late 2006. I am delighted with the performance, warm air during winter and great cooling during summer. I think it is costing too much to run. I am nearly certain it will break in the middle of winter. I am preparing to choose between a 3.5 ton and 4 ton replacement system. With the cost of energy going up, this older gear has to go, even though it is still running.
My wife's right I only use half my brain! I did not get the point of your question right, and maybe still don't.
Only to make you earn your lager:
Another way to measure flow is to measure air pressure differential in a duct of known dimensions/shape. This is inexpensive.
I would not try to measure capacity using the air stream, unless itīs an air conditioner in a building with many branches.
In this case it's easier to estimate capacity on the refrigeration side and then distribute this capacity proportional to air pressure drop of the same amount of equal duct or make flow measurements and divide total capacity proportional to the different flows.
This method may be as bad as any but should not be that difficult.
If what you ar trying to do is measure capacity of an evaporator and you have a heater it is easier to heat the air on the evap until the temperature leaving the heater is the same as the temp of the air in the coil. Then measure the heater power. But for this you need an autotransformer.
But if it realle were an evaporator you want to measure, what for? If it is product you want to cool then measure capacity there. It won't be the evaporator capacity but it's usefull effect.
OK, another (better) way to earn it is jogging after your lager. Cheers!