breezy_moto
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Can anyone provide some guidance with this problem? Really struggling with where the 62F comes from and how the reheat process line is drawn.
Thanks!
Thanks!
The air conditioning unit has a cooling coil which discharges the air at condition CC (CC in this case is 52db,51wb). Then, there is a reheat coil which performs simple heating (constant humidity ratio) until the desired room supply condition is achieved. Let's call this condition (S). We only know S will be to the right of CC, so locate CC on the psych chart and draw a horizontal line through CC. This horizontal line is the reheat process, and is shown in green in the chart below. S will be somewhere on this line to the right of CC.Can anyone provide some guidance with this problem? Really struggling with where the 62F comes from and how the reheat process line is drawn.
Thanks!
Ah! Thank you for the detailed explanation! I was missing the reheat concept of constant humidity ratio.The air conditioning unit has a cooling coil which discharges the air at condition CC (CC in this case is 52db,51wb). Then, there is a reheat coil which performs simple heating (constant humidity ratio) until the desired room supply condition is achieved. Let's call this condition (S). We only know S will be to the right of CC, so locate CC on the psych chart and draw a horizontal line through CC. This horizontal line is the reheat process, and is shown in green in the chart below. S will be somewhere on this line to the right of CC.
You are also given the room (or return) air condition which we will call (R) and is 75db, 50%rh. We know the air process as it goes from the supply registers to the return grills is a straight line from (S) to (R) with a slope given by the SHR of 0.66. Therefore, locate (R) on the psych chart and draw through it a line with SHR=0.66, which is shown as a dark blue line in the chart (you need a psych chart with a protractor). We know (S) will be on this line to the left of (R).
Therefore, (S) will be at the intersection of these two lines. That's how you obtain the 62F. You can calculate the heat required for the CC-S process by reading the enthalpy change directly from the chart, or by using an equation like they did in their solution.
View attachment 10892
You're welcome. Have you checked out the free sample pages (20+ pages) from our Psychrometrics and HVAC System Calcs for the HVACR Exam Study Problems book? This topic (and many more) are thoroughly discussed there. You can download the free sample pages HEREAh! Thank you for the detailed explanation! I was missing the reheat concept of constant humidity ratio.
I'll check it out. Was actually thinking of purchasing your practice exam solutions and working through your exam once I get through the NCEES exam.You're welcome. Have you checked out the free sample pages (20+ pages) from our Psychrometrics and HVAC System Calcs for the HVACR Exam Study Problems book? This topic (and many more) are thoroughly discussed there. You can download the free sample pages HERE
Cool. Keep in mind, though, that our exam is TFS; we don’t have an HVACR exam yet.I'll check it out. Was actually thinking of purchasing your practice exam solutions and working through your exam once I get through the NCEES exam.
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