Psychometic Problems while being prohibited from marking materials

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spacebanjo

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Hello,

Currently studying for Mech thermal/fluids exam in April. I am getting whooped by the MERM problems (although I understand they are much more difficult). In particular some problems require plotting Sensible heat /total Heat slopes on a psychometric chart (eg. MERM13 page 43-6 and 43-8 Recirculating Air Bypass).

I am unable to get these problems correct because I cannot plot the line slopes accurately as the scales are crude.  Furthermore, as I understand, during the exam we are prohibited from marking our reference materials which means we will not be allowed to plot lines on a psych chart --if there are multiple condition lines this would be a nightmare trying to finangle two rulers and keep them in place.

Anyone have tips for dealing with psychometric chart plotting? Am I missing some tools (compass, right angle etc) that might assist in this process?

Thanks,

 
It was my understanding that if solving a problem absolutely requires plotting on a psych chart, one would be provided in the exam booklet. 

 
Google Coolerado Psychrometric chart. Its a great chart that is colored and clearer than one in NCEES and MERM.

print several copies for marking on and use one unmarked one for the exam. I just slipped mine behind the clear plastic on back of my notes binder.

 
Hi spacebanjo,

I don't think you should be too worried about the SHR type questions, because I doubt that a testmaker would make possible exam solutions very close to one another, such that a slight difference in a SHR would cause a different exam solution.  Also you can break up the SHR into vertical (latent change) and a horizontal (sensible change) lines.  For example, if your SHR was 0.8, then you could arbitrarily choose a sensible load of 8,000 BTUH, total load of 10,000 BTUH and a latent load of 2,000 BTUH.  Then you could use the enthalpy and the dry bulb temperature to find a new point from your original point, with a SHR of 0.8.  I am not sure how much more detail I need to provide, but let me know if that makes sense.  

Also, just fyi, one of my old coworkers was removed from the test for marking up a psychrometric chart.

 
Justin thanks for the helpful comment. I think I understand -- that's a much better method than trying to eyeball parallel lines.

 
I used the attached chart, although there probably are much better versions out there.   I highlighted the major lines each in different colors to make it easier to read.   I took with me to the exam a clear plastic triangle and a 6" stainless steel rule.   With a combination of these tools, I didn't have to draw lines or make pencil marks on the sheet. 

View attachment Psychrometric Chart.PDF

 
I used the attached chart, although there probably are much better versions out there.   I highlighted the major lines each in different colors to make it easier to read.   I took with me to the exam a clear plastic triangle and a 6" stainless steel rule.   With a combination of these tools, I didn't have to draw lines or make pencil marks on the sheet. 

View attachment 9213
I made several copies of that one and used them for practice.

 
That ASHRAE chart appears to be identical to the chart that was included in the back of my exam booklet.  This is the chart I used to draw/write on during the exam.  

 
I just took the official 2017 practice exam - I can confirm they supply charts for air, refrigerant etc if it is required. 

 
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