1. Regular Guest
Join Date
Jul 2009
Posts
50
Post Likes

## SHR and ADP

Hi again guys

I know my room air specs, outside air specs and mixed air specs. How do I figure out the ADP or SHR of a cooling unit? Are those given values for a specif unit?

2. Regular Guest
Join Date
Jul 2009
Posts
50
Post Likes
I was told that most of the time for standard units we simply use a SHR of .70.

Is this correct?

3. Most mfrs. give you SHR of a given unit/coil match at ARI rating conditions of 95 out, 80/67 in. Pretty rare to be as low as .70 except Rheem & Trane. Could be a few others, but most tend to be .73 to .75.

Of course this is at extreme conditions. A cool, dry house on a warm day could be running mostly sensible since the system adjusts to conditions. A steamy house could run a high latent til it dries out.

4. Regular Guest
Join Date
Jul 2009
Posts
50
Post Likes
Is there a way to acculate calculate the SHR if I don't have the unit's spec sheet?

5. If you want to know a snap shot then yes but it is not easy as you'd think

First you would need to know the airflow, not a guess but the real airflow.

Once you have that, you can do a simple temp drop sensible calculation.

Then you would do a wet bulb drop, plot the readings on a phycometric chart to get the enthalpy and do the math to determine total capacity and subtract the sensible from the total. The divide the sensible by the total. IE Sensible 26,239/ Total 35,837= 0.732...

Total Heat Formula:
BTUH=CFM*4.5*(H1-H2) where H is enthalpy.

Sensible Heat Formula
BTUH= CFM*(T1-T2)*1.08 where T is temperature

Of course that's at sea level to 2000 feet you would have to adjust the constants (4.5 and 1.08) at higher altitudes.

Remember this calculation is just a snap shot not an indication of the system's potential and the accuracy of your instruments and readings are crucial. I would take multiple readings, especially on the enthalpy and average them.

6. you need the entering and leaving air condition as a minimum, plot them on a pyschrometric chart

you connect the two points with a line then extend the line all the way to the 'far left' of the page

you can get the SHR from the slope of the line, you get the ADP by reading off where it cuts the "100% RH" line and it is a snap shot as doc said

if the room is cooler or dryer than 80F at 51% RH the numbers will be different than any mfg rating

7. Regular Guest
Join Date
Jul 2009
Posts
50
Post Likes
In other words it’s easier and more precise to get the SHR from the manufacturer of the unit.

Next question is the temperature of Freon inside the cooling coil, SST and TD… what is the relation to the ADP. And If I know that info I can determine the SHR.

8. I view ADP as the average coil surface temperature, and average of the tube and fin temperature. The refrigerant will be boiling at a lower temperature than the ADP

9. Carnak... Werent you working in Aruba? I was just there and didnt see you anywhere

Then again, I wasnt looking, I was too busy sipping Mimosa's. (Was at the Rennisance).

10. caymans

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•

## Related Forums

The place where Electrical professionals meet.