Indicated ADP & Selected ADP 1

[redif]

Can someone explain the following in refrence to Carrier E-20 method of Cooling load Calculations

1. What is the diffrence in "Indicated ADP" and "Selected ADP".

2. What are the criterion for selecting the "Selected ADP"

3. What is the effect of Selected ADP on the SHR line, Cooling Load and Air Flow.

Thanks

 

[imok2]

1. What is the diffrence in "Indicated ADP" and "Selected ADP".
Ans. the difference is that the selscted ADP is determined by Carrier's soft ware where there are many more variables taken into consideration when designing the cooling coil.
2.What are the criterion for selecting the "Selected ADP"
Ans. The criteria is based on the input given the software
3. What is the effect of Selected ADP on the SHR line, Cooling Load and Air Flow.
Ans, the effect is a better design ot the cooling coil under a yearly projection of variables taken into account.( greater efficiency under more variable conditions)

 

[redif]

It seems my question was not very clear. My question is not related to Carrier HAP program but is related to the more fundamental concept in relation E20 Carrier manual calculation form. I try to be more clear with following illustration.

System : Chilled water with 44/54 deg delta T
Application : Conference room
Load : High Latent Load
ADP as selected from Carrier handbook : 40 deg F for calculated ESHR

Since the ADP is low than the chilled water supply temperature, to achieve the correct humidity it is necessary to add Reheat

Now what I want to know

1. What are the criterion to select a suitable ADP

2. Now since we have changed the ADP, the SHR line will shift and to achieve the original SHR we have to add some sensible heat (or Reheat). When new ESHR (corresponding to selected ADP) is matched by adding reheat to sensible load, then

a. Do we have to recalculate the dehumidified air flow for ERSH + Reheat.

b. Will this Reheat will be added to the total cooling.

Thanks

 

[imok2]

This statement cannot be:"Since the ADP is lower than the chilled water supply temperature" you cannot have the ADP lower then the chilled water supply.

"What are the criterion to select a suitable ADP"
I do not work with Carrier software' however the criteria in determining the ADP is a function of the total heat you are trying to remove. For example, in this conference room say if the sensible heat load is 35,000btu/hr and the latent is 18,000btu/hr(sensible heat ratio) total =53,000btu/hr. that's pt (1) on the psyc chart. Point (2) would be determined by the chilled water temp in and out of the coil, so if we say 56*F and 90% RH air off and we plot these points on the chart, we extend this line to the saturation line...that would determine the proper ADP temp, etc etc. Now that is the traditional way, However, Carrier claims that it has in it,s software a better design of the cooling coil under a yearly projection of variables taken into account.( greater efficiency under more variable conditions)Redif, If the answer is not sufficient then maybe someone smarter then me can help you.

 

[wilg]

Carrier indicates Aparatus dewpoints in thier
System Design Manual, page 1-145..table 65.
As Imok points out plotting the points out to
the saturation line is the established traditional
method and that's the indicated ADP, the indicated
represents the lowest effective sensible heat factor
(ESHF) possible (greatest slope).

However Carrier's design manual has different values for ADP if Reheat is added or actual coil effiencies
are in the mix, that's the selected ADP.

There is an equation on page 1-147, for ESHF which
includes ADP as a variable, by rearrangement and
solving for ADP you work the ADP out and investigate the
relationships of all the variables involved.
If you want me to, I'll rearrange it for you and place it
in this thread.

 

[imok2]

wilg, I have a few questions for you if you don't mind?
1, Do you use this method in your calculations?
2, Do you believe that the standard method is that far off for the average say..commercial building or small office building.
3 I do like the idea of future predictability if as a matter of fact it's really possible.
4, Like all these things however, its only as good as who is inputting the numbers. Your comments on these and any thing else are welcome for an old dog whose always trying to learn some thing he doesn't know.

 

[SAK9]

Redif,

In this type of situations with high latent load(conference rooms,restaurants,dance halls etc)you need to add reheat to raise the Sensible Heat Factor.With SHF raised,you can get a higher ADP and use 44F CHW.I remember doing this by a trial and error method until you achieve a RH of about 55%.

 

[wilg]

Imok,
Answer to your questions....
1, Do you use this method in your calculations?
Carrier seems to be the only Manufacturer that uses the Apparatus Dew point as part of their coil selection, they include a bypass factor, which is the psychrometric difference between the actual discharge temperature off the coil and the apparatus dew point on the saturation line,this bypass factor is a ratio of the entire length of the psychrometric line from the coil entering conditions to the saturation line as the denominator, and the length of the actual discharge conditions measured out to the saturation line.
Aerofin software and Heatcraft software do not indicate bypass factors or Apparatus dew points.
Trane does not include bypass factors or Apparatus dew points in their design book.
I know how to calculate it, but normally I use the manufacturer’s software, in the old days and I go way back, (I’m way beyond the point where normal people retire), you went to the manufacturer’s catalog and looked up his procedure for sizing the vendor’s equipment and every manufacturer had a different way of sizing airhandlers and coils, and then we did everything by hand calculation, (before calculators).

2, Do you believe that the standard method is that far off for the average say commercial building or small office building.
No, I don’t believe that the standard method is far off. The thing I really don’t like is seeing general rules of thumb being used, and the “if some’s good, more’s better” approach that a lot of engineers throw in, if I could stamp out over sizing of equipment I would. Math and physics should be applied in a scientific manner. Most of the time people throw in a lot of extra capacity and then wonder why the equipment is short cycling.

3. I do like the idea of future predictability if as a matter of fact it's really possible.
Future predictability, = we do the best that we can.

4, Like all these things however, its only as good as who is inputting the numbers. Your comments on these and any thing else are welcome for an old dog whose always trying to learn some thing he doesn't know.
You’re a part time teacher and worth an awful lot, I’ve read your comments on HVAC and they indicate a lot of experience, keep up the good work.
wilg

 

[quark]

Redif!

To simplify the answer you need not have to recalculate the dehumidied air flow when you change the ADP but your cooling load increases. (which is the mass flow rate of air times enthalpy difference of mixed air and the new saturation point)

Just note that required moisture removal can be done by either increasing air flow or by reducing the moisture level in the treated air further. The problem with increased air flow is that you may not be able to maintain the area DBT if coil size is fixed.

In our case we are reducing the treated air moisture level by reducing the saturation point. This will cool your air further and that is why you have to increase it's sensible heat.

Regards,

 

[imok2]

Wilg, thanks for the response and the kind words.