Estimating Fuel Cost for Heated Driveway

Tom Anderson

Have heated slab in northen Vermont.... and I have been requested to estimate annual fuel costs.

Looking for guidance on appropriate methodology. I have both degree day data and bin hour data available.

Installing contractor has provided the following information:

Square feet of heated slab

6" concrete

2 inches rigid foam underneath

Design outside air temp

Design Btuh for entire slab

50% glycol solution

Heating runs continually when outside air is below 32F. Intent of heating is snowmelt for safety reasons.

Wondering if I could use degree days, working out the Btu per degree for the entire slab. Or use bin method. Or, is there another acceptable method to use?

This type of heating estimate is a new one for me and appreciate any assistance.

Chris Maderia

Fuel Cost

What is your heat source? Your BTU's per sqft should be minimum of 110. I know that Viessmann has developed a software program for fuel consumption comparisons that they use when quoting on commercial jobs. I would try to contact them.

RB_2

ASHRAE

Go to ASHRAE Applications Handbook, Chapter 49. for a complete method.

Have had client’s request similar information, which we provided, but with some type of caveat stating weather data and energy costs are unpredictable and as such calculation is provided as information only. The user or any third party shall hold provider of information harmless for any reliance on said estimate.

The last thing anyone needs is to provide an estimate of energy consumption then have an extreme winter with rising oil prices...some clients will try to make others responsible for things which are out of our control…. like an excessive fuel bill.

RB

Tom Anderson

Results

RB: Thank you very much. You saved my butt.

My results were as follows, for northern Vermont:

Asssuming 80% boiler efficiency; heating runs constant below 32F ambient; 2" rigid insul undeneath,

Oil, 1.9 Gallons per square foot per year

Wood chip fuel, 50% moisture, .033 tons per square foot per year.

Application is at the state capitol, where a central wood fired boiler plant heats the capitol campus.

Thanks again!

Tom Anderson

RB_2

No problem

been through a few mine fields...some you just have to avoid.
RB