Heating and cooling load calculations in Revit MEP

[Mehdi.Kardehi]

Hi All,

Couple of questions with this?

- Do you trust Revit heating and cooling calculations? I mean after you modify all the building materials and weather information do you do your calcs with Revit or a third party laod calculation software?

- How about duct and pipe sizing? Most of consultants do those with other tools.

- I have been exporting revit spaces as gbXml to E-20 to do the load cals but I need to mannually input all those calcs back into Revit. Is there a faster way of doings that?

- And lastly most of the clients don't like the way Revit shows the calculations Report. Is there a way to customise those outputs and get them shown in the way I want?

Cheers,

Mehdi

[russellvee]

Yeah, that was it... When I change the space and building occupancy profile to ON - 24 hours it plugs in a full 100% human being into the room. I didn't realize the load profiles could have partial occupancy throughout the day. Seems like a dangerous assumption to me. According to the common office load profile, an office with an occupancy of 1 person will never have more than 95% of a person in it.

[mmcglone]

A typical office will never have a 100% of a person.  For me at least 5% of myself is always golfing. 😉  Looks like revit load calcs are out of the question until they get some changes/improvements implemented.

[revit_thug]

Back in school we did all this in Excel. It was actually quite helpful to know how things are actually done 😃

[fredULB]

Nothing seems to have changed in Revit 2015. I really feel MEP people are completely forgotten.

for example, still no heat loss coming from the floor  (only terrible solution => http://forums.autodesk.com/t5/Revit-MEP/Heat-loss-through-basement-wall-semi-exposed-basement/td-p/3... ) !

Seems that Autodesk people never got the freezing feet symptom...

[revitworkbench]

What I am seeing is actually the other direction with people, I put 90 people into the space and got 6375.6 Btu/h which is 70.84 Btu/h when its set to 250 btu/h. Does anyone know why Revit doesnt follow its own parameters here? Any POSSIBLE explanations of why sensible and latent load calculations dont meet revits own parameters under the

[russellvee]

This sounds like the same issue I had. It is probably because of the space type you have assigned to the space. Even though you told it there were 90 people, Revit assigns an occupancy schedule with an hourly percentage and checks that against your hourly load. So if I assign a space as a Hotel/Conference Center with 90 people and "24 Hour Hotel Occupancy", Revit just goes ahead and assumes that the room is only 20% loaded (18 people) from 9AM-2PM, etc.

THIS IS HORRIBLE AUTODESK!!!!! DO YOU REALIZE HOW AWFUL THIS IS!!! I HAVE DESIGNED MULTIMILLION DOLLAR BUILDINGS WITH THIS AWFUL, AWFUL SOFTWARE. JUST GET RID OF THE LOAD CALCULATION TOOL IF YOU'RE NOT GOING TO DO EVEN MINIMAL IMPROVEMENTS TO MAKE IT FUNCTIONAL. STOP WASTING YOUR TIME ON THE ENERGY ANALYSIS TOOL IF YOU CAN'T EVEN GET BLOCK LOAD CALCULATION CORRECT!!!!!

[revitworkbench]

Ok, Well I see that revit seems to be taking my occupancy % from the time of day that my peak load falls on. Since it says it is at 5 pm in July. But if it is a night time schedule, which starts total capacity after 7pm why would it assume max load before people get there? And what the heck are they doing with latent load calcs? They are like 40% of total load and it can only be 30% max....?

[russellvee]

Its because of your window load. The sun shines the most in your west facing windows at 5pm and is probably the biggest factor in your sizing, but the people don't get there until 10pm when the sun is down. In the hotel conference room example above, if I have lots of south facing windows it will always figure the peak load sometime during midday, when it says the room is only 20% occupied. And we know hotel conference rooms would never be fully occupied at noon when the sun is shining in all the windows, right? The way you enter the number of people is very misleading unless you are aware of this factor. I changed all my space type occupancy schedules to ON 24 HOURS with 100% load for all 24 hours. I want the worst case scenario, and I really don't care about the energy analysis function that Autodesk spends so much effort improving because who would dare trust the results when the whole thing is built on faulty calculations .

[russellvee]

Also on Latent Cooling Load, Revit will not help you with selecting proper equipment with a suitable Sensible Heat Ratio to meet the latent needs of your space. They will only give you the total (Sensible + Latent) load to use in your schedules. So there is no easy way to check your latent load without searching through the 500 page load report and using a pencil to write down the latent load for each zone, then comparing it to the total load to see if you will need to use larger equipment to meet the latent load. If they were to simply allow us to put the latent and sensible load components in a schedule, then we could use a calculated value to determine what the properly sized zone equipment would be to meet both the sensible and latent loads.

I'm not sure if anyone at Autodesk even understands what a sensible heat ratio is. I don't think they've ever talked to anyone who designs building MEP for a living.

[revitworkbench]

Ok, I give up will someone PLEASE tell me where revit is getting its Peak Airflow from? Like what is the equation it is using and what are the variables it plugs in? I must be missing something because using the parameters that I set, and Q=1.08(CFM)(delta T) Revit is consistently like 30% too low on what they say the peak airflow is. It is a saturday though, so maybe my brain is taking the weekend off...please help!

[MedaKaja]

Does Autodesk have solution for these problem?

[Mehdi.Kardehi]

I think we should all wait for another year until we hear something from Autodesk on this !:|

[ondrej.uher]

Hello,

do you have any news about this topic? I tried to do some calculations according to verified examples and heating and cooling loads where much bigger than they should be. 

My question is, what is it working in Revit MEP? Because heating and cooling calculations are not working and pressure drop calculations are strange too. For me is it just 3D program for checking collisions.

[Neldeguzman]

Thats why we have diffirent formula to follows and consider based on direction and location or area.

[michele.argenta]

you save me!! thank you so much 🙂

[jdipasquale]

Does anyone know if this issue has been resolved in Revit 2017?

[davidmeblack]

jdip - I was just about to ask the exact same thing - starting a massive project in a few months and would love to be able to use Revit to its fullest extent! Anyone have info on this???

[mohammedjazim25]

Is it possible to edit the u values of components in revit ???

[ec-152]

I think they don't are interested in HVAC calculation. Program have the same problems. 

[safakgunes]

Still no official answer? Interesting...