Delta T

J Matthers_2

What is an optimal Delta T between supply and return? Do you want a large Delta T or a small one? My thinking is if you have a large one you are giving up more BTU’s to the space you are heating. I have been told otherwise, however, and that if I have a large Delta T I need to increase the rate of flow. The areas that have the large Delta T are no getting enough heat but should be according to the heat loss calcs. What are your thoughts?

Steve Eayrs

Large or small Delta T????? Depends on a lot of things. Type of boiler, design, etc...

Condensating boilers like colder returns (larger T), most other boilers don't. You have to stay within the design of the boiler itself.

Controls/pumps/pipe size, etc...of course all play a part in this. There is not an answer that fits all applications to your question.


You are correct saying that increased flow will decrease the delta T, but within reason a bigger pump is not always the answer. Depends of the rest of the problem. Heat load, pipe size, supply temp. needed, p/s piping?, etc...


Steve

hr

I think

you are talking about the radiant floor loops? Most design software builds around a 10 delta t on residential. Large commercial or warehouse spaces may go as high as 30°, where consistant floor temperature in not an issue. Some striping is not objectionable in these cases.

The load will determine the delta t you are seeing. A cold room will spread the delta t wider and as the room approches setpoint the delta t narrows.

You will see this big time when you start a cold slab in mid winter, or a snowmelt on inital start up.

I agree the wider delta T will deliver more BTU's, do the math. You can deliver 100, 150 or more btus to a square foot of concrete outside in a snowmelt application at 32°slab temperature. Probably not in a 60° inside room

hot rod

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