Unit Conversions the Easy(ier) Way

If you work in facilities management, you know the struggle. It’s common to have utilities measured in one unit and billed in another, especially if you have some older meters onsite. And if you want to evaluate efficiency or compare energy usage, you need to convert all your energy consumption into BTUs (or British thermal units) so that you’re adding and comparing apples to apples as you move from chilled water to plug loads to boilers.

Converting from one unit to another is often harder than it sounds, such as for gas and steam, because it's not just one step or the same conversion factor every time. We've addressed both billing conversions and BTU conversions in previous articles. This time we've pulled these related topics together to provide an overarching guide to conversions, with all the most common unit conversion info in one table. Think of it as one table to convert them all.

Converting to Billing Units

Often meters measure a utility in one unit but the utility provider bills in something else. For example, domestic water is usually measured in gallons but billed in hundreds of cubic feet (abbreviated to either HCF or CCF, depending on the provider's preferences). A hundred cubic feet of water is the same as 748 gallons. So to convert a meter reading in gallons to cubic feet, you just divide the number of gallons by 748.

The table below shows common conversions in facilities management.? Factors for converting to common billing units are shown in the green column.

Converting to kBTU

If you want to evaluate your efficiency of operations, you need to be able to add up consumption from different utilities. The way to do that is to convert everything to kBTUs.

For some fuel types, the conversion to BTU is straightforward (shown in the red column in the table). For example, 1 kWh of electricity is 3.412 kBTU. For chilled water, 1 ton/hour is 12.008 kBTU.

Once everything is in BTUs, you can compare equipment efficiency and add everything up to get a sense of energy use over time. For example, maybe you need to convert to BTU to compare the ongoing efficiency of a gas boiler to an electric one, or to total up all your energy usage across the building (see the chalkboard example below).

What kinds of situations benefit from BTU comparisons?

• Cost allocations
• Energy use index (EUI)
• Equipment sizing and purchasing

Here's an example that pulls it all together:

Converting Steam & Gas to BTU

Converting electricity or water to BTU is usually straightforward. However, other energy sources, most commonly steam and natural gas, don’t convert quite so painlessly. Complications arise for three reasons:

1. Variation in fuel quality?
2. Terms of the lease contract?
3. Pressure of delivered utility vs. pressure during operation?

Calculating the cost per BTU for steam and natural gas is often dicey because the fuel source is delivered at one pressure but used at a different pressure, and the pressure affects the energy content of the fuel. For example, steam in NYC is delivered at 165 pounds per square inch. But a heat exchanger can operate at pressures as low as 5 psi. Which pressure value should you use to calculate your tenant’s share of the utility costs: (a) the pressure delivered or (b) the pressure at the point energy is consumed?

We’ve even seen tenants who want to subtract out the energy consumed by the conversion of steam to water in the heat exchanger before they pay their bill. Money is won or lost in these contractual details.

Converting natural gas to BTU has the same issues of delivery pressure as steam, plus the energy content of the gas. The quality of the gas can vary both by region and from month to month.

The first place to look for the energy content of your natural gas is your building’s monthly utility bill. If it’s not listed on the bill, you may have to contact your utility provider to get these values. Also, utility providers can change their sources at any time, which can mess up any meaningful evaluation of efficiency if not caught and corrected, which is why it's helpful to check these factors regularly.

Questions to Consider in Efficiency Calculations

• Where do your energy content numbers come from? Does your utility always provide the BTU and pressure values for the energy sources your facility uses?
• Do your lease terms spell out the BTU calculations for your fuel types? Do you want to change the way BTUs are calculated in new leases??

Final Recommendation

Unit conversions are the gremlins of utility calculations, always ready to get in your way. If you calculate your billing packages internally, we recommend explicitly entering the conversion factors for steam and gas each time, rather than burying a value in a formula. Otherwise, a minor error may blow up your entire mission.