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Manual J vs Ekotrope Load Calc

This forum is for any questions related to the HERS industry.

3/26/2020 12:34:34 PM
View user profile for Daniel Jarmolowicz
Total Posts 2

Manual J vs Ekotrope Load Calc

Hello,

I frequently find that Manual J reports provided by HVAC companies are much higher than what Ekotrope estimates in the Energy Design Loads Side Bar. I've found window areas to be way off and not the correct U or SHGC. I've seen occupants 20+ to inflate cooling load. What I'm getting at is how close should the manual J and a modeling software's calcs be? Are we as raters missing something or is the HVAC industry trying to avoid the callback for when the system doesn't keep up beyond design temperatures? At the end of the day it's the HVAC contractor who is installing and standing behind the system, but seems like something that could be improved in the industry.

Thank you,

Dan Jarmolowicz 

3/26/2020 2:09:25 PM
View user profile for Chris Mazzola
Total Posts 14

Re: Manual J vs Ekotrope Load Calc

Hi Dan,

Great question , this has been an issue with Manual J software and the HERs softwares (REMRate, Ekotrope and even EnergyGage) never really matching up, I guess the most common explanation is that the Energy model does not model the sensible and latent heating load quit right and the manual J software does not use current infiltration rates. both are pretty significant entries. I typically look at both and compare them to this rule of thumb, ( super scientific: 1 tom /1000 sqft of CFA) if your with reason or 15%, I am OK with It. remember, we are responsible to "do our do diligence" a grossly over or under sized system will present there own issues, avoidance of that is the goal, reporting that is our job. 

both software developers have great support, Ekotrope and REMRate. support@ekotrope.com and bchristensen@noresco.com if you need additional specific help or questions.

3/26/2020 2:10:40 PM
View user profile for Chris Mazzola
Total Posts 14

Re: Manual J vs Ekotrope Load Calc

i would love to hear the opinions of some of the other long time more Sr, raters - what is your take on sizing in general...

3/26/2020 3:23:06 PM
View user profile for Jay Smith
Total Posts 2

Re: Manual J vs Ekotrope Load Calc

Hi,

With out getting to technical (it hurts my brain), off the top of my head Ekotrope, and Remrate are rating software and are not approved for heating load calculations, there is probably a reason why? Have you ever noticed how low the annual cooling costs are?

I also do occasional Manual J calculations with WrightSoft, even when I use all the same calculations and values Wrightsoft usually comes up with a larger load requirement. You are able to specify the infiltration in Wrightsoft and I set it at 3 ach50. The more I learn about equipment sizing it is all about the latent cooling capacity and duct design.

Anyone including me can buy Manual J software and produce a report, there software is not exclusive to Mechanical Engineers as Rating software is to raters. Until you have to be certified to do Manual J calculations you will see many conflicting reports.

I for one am excited for Resnet/ACCA/ANSI Standard 310 and the HVAC Quality Installation Commissioning Check list being implemented this should help move us in the right direction.

3/26/2020 3:34:32 PM
View user profile for Chris Mazzola
Total Posts 14

Re: Manual J vs Ekotrope Load Calc

thanks Jay,

great insight and totally on point. I think we should all be excited to see commissioning coming in under our scope, i am not looking forward to the extra work, but it does allow for a path to mandate corrective action. it will be important to get a standardized testing protocol out to the rater community ASAP so we are consistent across the region. A great webinar for Rich to work on putting together for later this year.

i also would like to remind everyone, we are verifiers when it comes to sizing, the manual J should be coming from a trusted and certified source (eg. mechanical engineer). it is typically obvious when it is not and an easy flag to the municipal inspection dept when it needs to be redone.