Everyone, I have a building in Fairbanks Alaska that uses hot water
heat. I built an energy model for it and included a gas, natural draft,
80% efficient boiler to heat the hot water. I then deleted the gas hot
water boiler and substituted a steam meter. I repeated this process for
the gas DHW heater. When I ran the steam heat meter energy model, I
noticed that the Heating Energy Consumption was reduced by 38% compared
to the gas energy model. Nothing else seemed to change much, but the
reduction of heating energy bothers me. I realize that a steam to hot
water heat exchanger is more efficient than a boiler, but why does the
amount of heating energy required drop so much? Shouldn't the amount of
heat required be the same for both models? I have attached the Energy
Consumption reports for both models. Thanks.
Kathryn Kerns
I had the same problem when I wanted to use a steam meter on a DHW loop. The only thing I can think of is that the steam meter doesn't account for storage losses. It does seem like a suspiciously large difference, though.
Kelsey Van Tassel
Isn't this difference simply accounting for the inefficiency of the boiler? The loads on your HW loops should be the same between the two runs and should match what the steam meter reports. But these don't account for the inefficiency of the steam boiler: 80% combustion efficiency plus losses through the jacket, cycling, and pilot. If you could model a steam boiler, upstream of your steam meter, there would be losses there too that are not being accounted for in your comparison.
Date: Wed, 28 Apr 2010 09:33:19 -0700
From: kathryn.kerns at bceengineers.com
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Steam Meter Energy Usage Much Less Than Gas Boiler Energy Usage
Everyone, I have a building in Fairbanks Alaska that uses hot water heat. I built an energy model for it and included a gas, natural draft, 80% efficient boiler to heat the hot water. I then deleted the gas hot water boiler and substituted a steam meter. I repeated this process for the gas DHW heater. When I ran the steam heat meter energy model, I noticed that the Heating Energy Consumption was reduced by 38% compared to the gas energy model. Nothing else seemed to change much, but the reduction of heating energy bothers me. I realize that a steam to hot water heat exchanger is more efficient than a boiler, but why does the amount of heating energy required drop so much? Shouldn?t the amount of heat required be the same for both models? I have attached the Energy Consumption reports for both models. Thanks.
Kathryn Kerns
A steam meter assumes that you are using steam from a district plant and
hence would not equal the gas load to a boiler. The steam is made outside
your model so the heat loss for the steam plant is not included.
Sincerely,
Reinhardt Associates, Inc