6 min solutions HVAC
Posted 03 April 2012 - 08:40 PM
Posted 04 April 2012 - 03:15 AM
I plan to take the NCEES test this Friday, I'm hoping for 80 to 90%. I'll use the remaining few days to practice problem areas, but plan to do no problems or studying after Tuesday.
Ready or not, exam time is upon us. Good luck all!
Posted 04 April 2012 - 11:55 AM
Posted 07 April 2012 - 10:40 PM
Posted 08 April 2012 - 01:04 PM
Posted 08 April 2012 - 06:38 PM
Posted 09 April 2012 - 03:44 AM
I thought the NCEES was tougher but I think it was only because I'm weak at power cycles. There weren't many of those in the 6ms book.
Check out the ASHRAE fundamentals chapter on thermodynamics and refrigeration cycles. It is much better than the MERM refrigeration cycle section. It has a good chart showing the cycle in a pressure - enthalpy, a good set of equations for everything that was asked in the practice test. Along with a diagram showing the typical equipment. I read that page (7-8) in 2011 and was able to work all of the problems that I had trouble with in about 15 min.
Posted 09 April 2012 - 12:15 PM
Posted 09 April 2012 - 04:52 PM
Posted 09 April 2012 - 05:38 PM
Posted 09 April 2012 - 05:47 PM
Posted 09 April 2012 - 08:15 PM
it may be a good idea to bring this for the morning test. There is alot of good fan and duct design rules of thumb and guideline in there.
Here is a link to the refrigeration cycle cheat sheet that I made from the ASHRAE Thermodynamics section. It would have helped me in the NCEES practice test HVAC afternoon section on about 5 problems. let me know if it helps.
Posted 09 April 2012 - 09:02 PM
Posted 09 April 2012 - 09:14 PM
Posted 09 April 2012 - 09:39 PM
Posted 10 April 2012 - 04:03 PM
Posted 10 April 2012 - 04:46 PM
When trying to find the refrigerant mass flow, do you use Q2-3 or Q4-1? The MERM uses the evaporator mass flow and I haven't seen an equation for the condenser flow.
When adding superheat, is it just an isobaric process? Would supercooling just bring point 3 to the left?
Posted 10 April 2012 - 05:58 PM
You can really use 4q1, 2q3, or 1w2 if you know the enthalpy difference for that piece of equipment. The mass flow rates will be consistent through the system so once you figure it out for one portion of the cycle it is the same for all. Super heat on the compressor suction - Pt 1- will keep the same pressure as the evaporator just jump up in the temp. You can read the enthalpy directly from the chart see the two points on the chart for pt 1 , 1 is at sat. 1 is with 20F superheat. I am not as sure for the subcooling though. I would think it would do as you say but i am not sure.
Posted 10 April 2012 - 06:33 PM
0 user(s) are reading this topic
0 members, 0 guests, 0 anonymous users