More Best Practices
Part of an energy auditor’s job is energy analysis, which includes historical energy consumption data to determine if usage is as expected. One method is to compare a home’s energy use to some average—the local rural electricity provider I contract with calls this ‘compared to your neighbors’.” This average could be the national average, but it’s better to compare at a more local level, such as by state.
There are a few sources for this information including the U.S. Energy Information Administration – EIA – Independent Statistics and Analysis. This dashboard provides several energy consumption metrics, expressed in MMBtu and kWh, broken down by state; it also displays U.S. national averages. (Sorry, Canadian friends.)
Measuring energy use
Before we dive into the analysis, we should look at the two measurement units used to compare energy usage: Million British Thermal Units (MMBtu) and kilowatt-hours (kWh). One Btu is defined as the amount of energy required to raise the temperature of 1 lb. of water 1 degree; 1 MMBtu equals 1,000,000 Btu.
A watt is a unit of power, one joule (J) per second. As an energy auditor, I look for electricity consumed, which is billed by kWh, or 1000 watts per hour. We can convert kWh to Btu and vice-versa. One kWh equals 3412 Btu; 1 MMBtu is equal to a little more than 293 kWh.
Calculating energy use
Now that we have a basic understanding of the metrics we use for an energy analysis, let’s use the data to perform a basic energy assessment. We’ll use my home as an example (lead image). The house is located in northern Minnesota, Climate Zone 7. It has a conditioned floor area of 2054 sq. ft. It’s primary source of heat is a natural gas forced-air furnace (the only gas-burning appliance). There is also a central ducted…
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6 Comments
A 35 year old water heater, they don't make them like that anymore !! I always liked to use BTU's per square foot of conditioned space per heating degree day as a measure of energy efficiency. With metered gas a lot of data can be mined from daily, monthly and yearly gas meter readings. Quite easy to flesh out the non-heating portion of gas usage by taking summer readings as well. Btu/sf/hdd is a nice way to track incremental energy improvements for those of us who do a bit at a time. The Btu/sf/hdd measurement is also handy in doing side by side energy use comparison for heating of homes in a neighborhood or city.
Doug
I always enjoy Randy’s post — he did a great job on reviewing my house plans and offering suggestions!
For your air source heat pump water heater you might wish to use a split unit that prevents the heat stealing.
https://www.eco2waterheater.com/product-info
Solid information, as always.
Randy-
Any experience and thoughts with waste water heat recovery? I have one in my house with gauges and in the winter months when someone is taking a shower it pre-heats the incoming water by 15-20 degrees. Installed it 14 years ago, all copper, cost about $500 back then, has no moving parts and needs no maintenance.
Hi Jud,
I am familiar with wastewater heat recovery. Over the years I have worked on a few projects where they were installed. My understanding is that they have a faster payback when used in buildings where a lot of hot water is used, multi-family, laundry facilities, etc... but, if you are constructing a home with the plan of it being around for a century or more, why not.
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