Establishing performance of air to air recuperative heat exchanger

[CmAnD]

I am young mechanical engineer and I am a relatively new in this field, but in front of me is a very responsible task.

The company for which I work in the near future is starting with production of air to air recuperative heat exchangers. My task is to give a proposition for layout of equipment for evaluation of the performance of the heat exchangers in order to collect performance data.

I have done a lot of work until now but I have some questions about some of my doubts. So I will appreciate any suggestion about this issue.

Everything is clear for me when the dry effectiveness of heat exchanger is examined. You do one evaluation measurement with inlet conditions prescribed in the standards and you calculate all the necessary values. After that, you make another measurement with different inlet conditions without condensation (different combination of flow rates on exhaust and supply side) and you calculate the effectiveness and other necessary values. With this collected data you make correction factor that can be used for calculation of effectiveness and outlet temperatures for any combination of inlet flow rates on the side of exhaust and supply air.
But, as I can see at this stage of my knowledge, you cannot do the same when condensation occurs.
My question is: Do I need to make measurements for every combination of air flows rates and any combination of humidity values on the exhaust and supply air at different temperatures in order to collect data for whole working range of the heat exchanger?
If I must do it, how the equipment should look? Can I put all dryer, humidifier, heater and cooler in a duct line, or chambers should be build where the air with specified condition will be made and extracted from it and guided to the heat exchanger.
It sounds very hard for me!? Almost impossible!?
I ask myself how can you keep the state of equilibrium enough long to collect necessary data.
Maybe I have to learn some more theory of wet air?

I expect your comments and advices.

Thank you in advance!!!

 

[ChrisConley]

Sorry, I'm remote and don't have my reference materials at hand, but I believe ARI 1060 lists the requirements of testing air to air heat exchangers.

I may have the standard wrong, but ARI (AHRI now?) would be a good start.

 

[CmAnD]

I live in Europe and I guide myself according to EN 305, EN 306, EN 307 and EN 308 standard.
I also have ARI 1060. I have downloaded it for free, from ARI’s web site. Is this complete version?
EN standards are more precise than ARI 1060 standard, and everything that is prescribed in the standards is clear for me.

As I said in the first post, there are two kinds of inlet conditions that are prescribed In EN standards.

To establish performance without condensation:

Exhaust air:
Tdrybulb=25[oC] Twetbulb<14[oC]

Supply air:
Tdrybulb=5 [oC]

And there is no problem for me when condensation does not occur.

To establish the performance when condensation occurs, the following inlet condition are stated in EN 308 standard:

Exhaust air:
Tdrybulb=25[oC] Twetbulb<18[oC]

Supply air:
Tdrybulb=5 [oC]

And additional inlet conditions for making test for cold climates:
Exhaust air:
Tdrybulb=15[oC] Twetblb<10[oC]
Supply air:
Tdrybulb=-15 [oC]

And the NOTE after that, that confusing me:
“…NOTE: These input criteria are given for standard tests to verify performance data given by the manufacturer. However, the test method can be used to obtain rating data for a recovery device over the whole of its input range. …“

And that is all that is prescribed in the standard.

So, because we are the manufacturer, we must supply our customers with data for performances in whole input range.

The question is from theoretical nature.
Is it inevitable to make measurements for every combination of air flows rates and any combination of humidity values on the exhaust and supply air at different temperatures in order to collect data for whole working range of the heat exchanger?

The practical side of this issue is: If I must to do it, is it possible? How to do it? How to arrange the equipment?

I will appreciate very much any kind of advice.

 

[marcoh]

I would have thought you would provide air conditions (Cwb and Cdb) for outside air, supply air, return air, and exhaust air and note if condensation occurs. If condensation does occur the air stream is just dehumidified (ie will affect the Cwb of the air stream).

 

[CmAnD]

Hi marcoh,

I suppose that you want to point me something about the issue, but I can’t fully connect the things that you wrote, with my problem.
I would like to ask you if you’d like to give wider explanation of your point.
Please read carefully my previous posts to completely understand my problem.
Let’s say that I have data for one or two measurements with different inlet conditions.
Is it possible to predict the outlet condition of the air in whole input range of the heat exchanger when condensation occurs without additional measurements?
When I say whole input range I mean any combination of inlet conditions (temperature, humidity and air flow rate) on exhaust and supply side of the heat exchanger.