Choosing you heat exchanger...
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Karl_northwind
Minister of Fire
It depends..... I work with storage systems where low temperature is important, and as such, make sure that I can get the BTUs I need for all but the very worst days with 120F water temp, and have a 100F outgoing temp. that prevents feeling cold drafts, and allows good storage usage.
what are you heating, and what are you heating it with?
k
what are you heating, and what are you heating it with?
k
I'm heating 2700sf plus a heated basement of 1200sf. The unit being installed will be a woodmaster Fuel Flex kw30 wood/pellet gasifier. Wondering if there is any benefit of going higher than 140,000 btu's with the water to air heat exchanger going in my forced air system.
Karl_northwind
Minister of Fire
ignore the "rating" btu on the air HX. get a sheet from the manufacturer for the varying conditions, and work from that. the "rated" that I have seen is high air flow, high water flow and high water temp (180F). With a storage based system, look at the specs for the HX at 120-140 F water supply temp, ~1000 Cfm air flow and make sure the outgoing air is above 100F. then make sure that's enough BTU's delivered to keep the house warm at near design conditions.
my observation is that the HX's I have ratings for, and design sheets for, is that in the above conditions, the output on the HX will be about half of the "rated" output.
karl
my observation is that the HX's I have ratings for, and design sheets for, is that in the above conditions, the output on the HX will be about half of the "rated" output.
karl
98kx1927
Member
This is a question I've had for a while. When I look at the spec for heat exchangers like:
(broken link removed to http://www.ctwoodfurnace.com/PDF/V101.2%20VAL%20Air2Water_logo_pg2.pdf)
How do I read this to understand the output water temp? If I'm looking for 100kBTU at design temp, and want my outlet water to be 100F, and the furnace is blowing 1000cfm, which heat exchanger would I use? I just don't understand the nomenclature in the spec sheet. I just picked this spec sheet from google it isn't special, but it appears to be similar to others I've seen.
david
(broken link removed to http://www.ctwoodfurnace.com/PDF/V101.2%20VAL%20Air2Water_logo_pg2.pdf)
How do I read this to understand the output water temp? If I'm looking for 100kBTU at design temp, and want my outlet water to be 100F, and the furnace is blowing 1000cfm, which heat exchanger would I use? I just don't understand the nomenclature in the spec sheet. I just picked this spec sheet from google it isn't special, but it appears to be similar to others I've seen.
david
You have to calculate the leaving water temp from that spec sheet, they dont give it to you. You would pick one of the listed inlet temperatures, and use the formula BTU = 500 x GPM x (tin - tout) Solve that guy for your tout, and you can figure out the leaving water temp. That said, you are trying to get to several values that are off the spec sheet. It would be best to figure out what you want for your incoming water temp, and then contact a distributor/manufacturer and have them provide the data for your specific need.
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