OD reset and staging

Jens Sorensen

Tekmar rep says OD reset will save 12.6% and staging of 3 boiler will save additional 5%. Do these numbers seem right? (Local City Hall building; City Council wants numbers for payback analysis. I'd prefer they be relatively accurate.)

Boilerpro_2

In my experience, they tend to be conservative

I specialize in church heating systems, and the savings over single input, non reset boilers, when installing 2 to 4 staged boilers, staging and reset controls and new setback controls throughout the structure usually run about 40% overall. Tekmar's number for savings due to staging of 3 boilers is probably based on the assumption that the single boiler is properly sized and the building load goes up linearly with outdoor temp. Well first, most single boilers are greatly oversized, so they are running at much lower efficiencies than they could and, when working in public buildings the heating load is anything but linear. Internal gains when the building is occuppied often dramatically reduce the heat load and night setbacks have the same effect, so a single input boiler will be running very inefficiently for most of the heating season. The pattern I've seen starts with the calculatd peak load plus a pick up factor. If you take that number and divide it by 3 to 4, this is the amount of capacity you need on a typical winter day and warmer... about 90% of the heating season. Since this comprises 90% of your heating season, this is the point at which you want your heating plant running a optimum efficiency.
Other selling points include built in automatic back up, often much simplier boilers sized under commercial code requirements (around me, under 400,000 input), improved comfort, and less wear on equipment due to less equipment cycling and lower average operating temps.
Just some of my experiences.


Boilerpro