Attention Wrightsoft Users!
Have you ever completed a load calculation and it just seems like it was short of what you had expected? Particularly when you are first starting out with a tool, contractors can make mistakes. After all, we tend to learn "the hard way", right? In an effort to make software work, the companies tend to start with some default values that require adjustment. For instance, most have the duct system in the conditioned space calculating zero gains or losses. If the ducts were in the attic, this could be as much as a one ton load that is missed! Internal gains tend to start at zero, and the foreground for windows is something between crushed rock and green grass. Most contractors find these values, over time and as they gain experience with the program. One still overlooked setting in Wrightsoft, a feature that no other ACCA approved software employs, is the Rate Swing Multiplier (RSM). This can cause you to lose as much as 11% of your sensible gains in an otherwise perfect load calculation, maybe more!
YES running loads is like rounding up kats. You very big knobs like south windows, open return in attics, unsealed supply's of building, I was at a new home 2 yr old this week - she claims the 1560 sf 4 spit 75,000 BTU/hr 2.5 ton AC is not big to H/C home. So I just ran a load and come up with 2/3 of that but when I ran the blower door a big -50 PA was 3020 CFM this home did not get sealed between walls where the plumbing comes up. The HVAC sheet steel installer got the wrap but I feel the low end builder got what he paid for. Then HVAC contractor just put in a 3 ton and 100,000 BTU and now will bid just this over sized "system".
My point is You must test out. I have used Wrightsoft for 20+ yr and I feel it over sizes 10-25% If you do not test out and redo the numbers. One of my .goals is to beat the 1st load. To test is find run time when the temp outside is at design temp - I look for 100% run time with out the heater hitting high limit. Gramps told me to size to -40 and I use now 0'. Now you see that systems get over sized