How do I calculate indirect heating loads

jp_2

sounds like you are saying above grade there is no insulation?

this makes a problem, if the outside of the footing is insulation only up to grade then 18" exposed, the below grade insulation doesn't do much. your perimeter slab then has a cold bridge to the elements.

a sketch of what you have would clear things up.

Mike Dunn

calculating indirect loads on the total envelope

I have a radiant project where the slab was poured directly up against a 4' footing wall that has 2" of rigid foam on the outside but none on the inside. There is 2" of rigid foam under the slab. Also, the slab resides about 18" below the top of the footing wall. On the outside of the building about 18" of the footing wall is exposed directly to the elements. This project is an addition to an existing building which also has a footing wall that the slab is poured up against with no thermal break. Design temp here in WI is -15 deg. The boiler cannot heat the slab up beyond 65 degrees and I'm wondering if alot of the btu's are being absorbed by the cold outside footing wall. If so how do I calculate approximately how many btu's I am adding to the heat load since the slab is not fully encapsulated.

Sorry for the novel but I wanted to get alot of details in.

hot_rod

Sounds like you do have a thermal break

and good r-value under the slab. It should be heatable... What does the heat load call for in terms of BTU/ hr load? Is the boiler and circulator sized top the load? All the loops purged and circulating.

I doubt that you are near outdoor design temperatures up there yet? You should be able to warm that slab just fine.

The Heat Load Pro software allows you to build in all thoase foam details when doing a load calc. It's helpful both for original design and troubleshooting.

Here is a picture of that screen.

hot rod

Mike Dunn

indirect heating loads

Heat loss was done with the Uponor ADS program. It came up with approximately a 72,000 btu heat loss with the system running at 7.2 gpm at 10 feet total head. All the loops have been purged and are circulating. The boiler is a Buderus GB 142-24. The circulator is a Grundfos UP15-42F set at speed 3.

I have set the boiler to run a supply temp of 120 but the boiler cannot exceed 100. The return temp just cannot come back warm enough so the boiler will increase the supply temp. Temps have been around 12 to 20 degrees for the last week.

The warmest I can get the room in a week is 60 and the warmest I can get the floor is 65.

If I draw a skecth of the insulation can I upload the file to this site as a pdf?