We submitted a single psych chart with coil conditions and comfort zone range (from 0.5 clo to 1.0 clo), and narrative. We filled out the LEED form with an operative temperature of 73°F for both summer and winter, and the operative temperature lands well into the comfort zone, but more towards the 1.0 clo side.
The project is mechanically conditioned and naturally ventilated. The project consists mainly of residential apartments. The unit has both heating and cooling capability. Humidity is not a concern in the project climate.
The comments we received state that the provided operative temperature of 73°F fall outside the comfort design criteria required by ASHRAE 55, and that we need to provide a narrative to explain why.
We did not indicate a demising line between the 0.5clo and 1.0clo, so the only response we can think of is to do a seperate psyc chart for summer, with a slightly higher setpoint/operative temperature and 0.5clo. This would indicate the deadband that occurs in T-stat settings. But, the review has not explicity stated anything regarding my assumption above, only that the operative temperature does not fall into the comfort criteria.
Lindsay Austrom
Mechanical EngineerStantec
21 thumbs up
December 19, 2012 - 1:47 pm
Brian, the summer condition at 73F and 0.5clo DOES fall outside the comfort parameters shown in Figure 5.2.1.1 of ASHRAE Standard 55-2004. What point(s) did you mark on the submitted psych chart? What design conditions did you specify for summer and for winter?
The summer design condition and winter design condition should each describe a single point on the psych chart, not a range. You could increase the operative temperature to fall within the 0.5clo zone, or you could use a higher clo value and interpolate using the equations in Section 5.2.1.1 of the standard. I think a 2nd psych chart (or one with both winter and summer conditions noted) should be acceptable.