This interests me, as lately I've been looking closely at how to leverage HVAC Zones and Spaces more fully. I've poked around at Revit's load calculation tool and decided that it wasn't something I was interested in. It's a joke compared to any stand-alone tool out there and needs several generations of improvement before it could be useful. What Autodesk needs to do is build a tool that's on par with Trane Trace or HAP, but I don't see that happening any time soon.

I also use HAP. I've been setting up my Spaces in Revit, and using Space Separator Lines to carve up the large Rooms into logical thermal zones (Perimeter, Interior, corridors adjacent to open offices, etc.) I also use HVAC Zones to group the Spaces and represent my Terminal Unit zoning. Then I do a gbXML export and bring it into HAP. This will give me Room Names/numbers, area, and occupancy (if I enter it before the export). The roof/wall/window data is simply garbage and I've stopped trying to get this to work, but hand-entering that data really isn't that bad. On a medium/large job, the gbXML export cuts the load calc time in half for me, even with its limitations.

As for heat loads, what I do is generate the Zone Summary in HAP, and enter the Heat Loads of each space into my Revit Spaces "Design Heating Load" parameter. Since it came from your gbXML export, there should be a rigid 1:1 relationship here. (I've looked into ways to automate this with Dynamo, but don't have the time to play with it) I can then create a Space schedule that's sorted by Zone, and turn on Footer Totals. This will give me the total heat load for each HVAC Zone, which I can then enter into my Terminal Unit families. From there, the Family will take that heat load value and parametrically size the reheat coil.

I'll check out this IES thing, it sounds interesting.

Thanks Necro99

quick question when u do your spaces in Revit do you calculate the area from centre of the core of the wall or the wall finish?
We normally do it to the centre but this client (UAE) wants it to be done from the wall finish ...the problem im having is that even if i change it in the "analyze space" to wall finish the area in revit is still incorrect...i.e if i use filled region in the space the area i get using the space tool and filled region area is different.
The filled region one is the more accurate out of the two.

Now im trying to find a way to tag my filled region so that the area shows up automatically like in a space tag but Revit doesnt give me that option...any ideas?

Can't be done without Dynamo. But I've created the attached DYN, as I needed this feature for something similar.
You'll need to add a Shared Project Parameter to Detail Items, called "DYN_FilledRegion_Area" (Or call it something else, but remember to change the string in the dyn file)
You´ll also need to create a tag that reads this "DYN_FilledRegion_Area" parameter.

Thanks Appreciate it