For most of my career, I have focused on energy management projects that reduce operational costs and have a quick payback. If you can improve efficiency by 20% for an asset that is used at least 3,000 hours a year, you can usually find a good ROI. Many technologies that can achieve this are available for lighting, boilers, chillers, motors, and other equipment, and many energy engineers can stay busy by improving the efficiencies of these heavily used assets.
However, before addressing efficiency, we must go back to basics and ask if an asset is needed at all. Often, there are mutually exclusive options between improving efficiency versus shutting off equipment when not needed. Think of it in terms of purchasing an item on sale: are there really savings if you didn’t need it in the first place?
To illustrate my point in an energy example, consider my all-electric house. Upon moving into it, we had a utility bill of $700. With great motivation, I sought to reduce the electric expense. I went into my usual mode of changing most of the lights to LEDs. I also put more insulation into the attic and adjusted the temperature setpoints (only slightly, to keep the spouse happy). Our bill was slashed in half. After some other projects, our bill has occasionally dropped to about $200. In all of these projects, I could almost see the energy wasting away, so the moves were common sense upgrades.PageBreak
Reaching for Higher Fruit
Even after reaching the $200 mark, I thought I could do better but didn’t know where to start. Wondering where all the energy was going, I invested in a real-time electricity submetering system for about $300. I installed the system in an afternoon by watching YouTube videos and following the instructions. It was actually pretty easy to install the clamp-on meters around the main electrical feeds (please be careful if you do this) and it was literally plug and play. You may need to buy a few dual pole circuit breakers, but that’s about it.
I used a product called The Energy Detective (TED) which allowed me to see real-time kW consumption and a whole bunch of other data (see the screenshots). I also downloaded a free app that displays the kW draw on my iPhone. This was handy because I quickly determined the kW draw of most major appliances by turning them on and off at the circuit breaker. Once that was done, I assigned load profiles for the major appliances and the TED system can guess when and which devices are on.
The next weekend, our family went on a road trip so I turned off the HVAC before we left. When I got back, I looked at the data and was intrigued by what was occurring while no one was home. The purple bars in the attached graph show the net kWh consumption, which was consistently about 22 kWh/day. If you do the math, this really isn’t that much, but the point is that it could be lower.
With a few clicks, I was able to investigate further and determine that the electric hot water heaters were coming on frequently (about every hour) all night, essentially heating water that nobody was going to use while we were away. The water heater graph shows this.PageBreak
Equipped with this data, I can now see an opportunity to save more energy, and I am excited to have a direction. I have been looking at heat-pump water heaters, waste heat recovery from the HVAC condensers, and other technologies to reduce the water heating costs (did I mention that I have a teenager?). I would love to do solar thermal, but our house is surrounded by tall trees and the shading is troublesome.
I’m considering the possibility of shutting off one water heater (or putting it on a timer). We may do this and/or install a heat-pump water heater in the basement, which would basically take heat from the large sealed basement crawl space and as a bonus, de-humidify it (which would reduce the potential for mold). I think there is enough surface contact area with the ground that this will function like a ground source heat pump, because the cold-dry air will absorb heat from the ground and this heat will eventually flow into the water tank. If I do the heat-pump water heater, which costs about $1,000, I can get a rebate of $300 from the utility and a 30% tax credit because the heat pump will move more energy than it uses (just like your air conditioner heat pump). I estimate my savings at $30 per month, so with incentives, this project will pay back in a little over one year.
There are many possibilities, but none would be clear to me without the data. Additionally, the ability to quickly determine the results of our efforts would be impossible without it. My advice for you is to obtain data – you may be surprised where it takes you. In commercial buildings, the savings (and costs of not having the data) are much higher.
Data can be obtained via meters, loggers, and other devices. Become an energy detective and consider the possibilities. Let me know what you find: [email protected].