GeekPi

Back in May, I declared an end to oppressive electric bills, never wanting to see another > $100 bill. Since then a lot has happened, and a lot more is about to be done to help reach the goal.

To give an idea of what I’m up against, I have a fairly typical 1970’s wood framed home. It’s a smaller 960 sq/ft and has only water and electric utilities. No natural gas  or sewer is available. Other than the occasional use of our wood burning fireplace, the main heat is provided by grossly inefficient baseboard electric. Even though the house has newer, double paned windows, it typically feels drafty and cold in the winter. That is likely attributed to the insulation, or lack thereof. The attic area has 6-9 inches of loose fiberglass, the walls have R-11 and the unconditioned, vented crawlspace has nothing. A lot of my heat is lost through the floor.

My wife and I moved in after our wedding, and being cash-strapped newlyweds, have been slowly updating as we go. Other than the windows and roof, all of the appliances and systems were original to the house. The problem for us is that the electric bill varies wildly in price and is directly correlated to the colder temperatures (as seen in graph to left). Our summertime bills were the most palatable, at an average of $50 to cover our baseload needs (water heat, light, A/V and PCs). During the peak of winter the bills would shoot up to the $200 range a month, with the baseboard heat accounting for $150 of that demand. We used programmable thermostats in each room, and only had the baseboard heat warm up to 70* during our mornings from 6am to 8am and then from 6pm to 10pm. The rest of the time, they were set back to a chilly 64*.

Welcome ductless heat-pump

After two cold and expensive winters, it was time to do something. Now I know that the first and most efficient place to look is to seal up leaks and improve insulation amounts. What threw a wrench into my plans is that our utility (Puget Sound Energy) was offering an exceptionally generous incentive of $2,000 for baseboard customers to install a ductless heat-pump. That, combined with a $1500 federal tax rebate made the heating system the most cost effective improvement in terms of return on investment. Over the summer, I’ve been working on sealing up air leaks with expanding foam and weatherstripping, and after the new year, when I’m eligible for the 2010 energy tax credit, I’ll contract out to have the underfloor insulation installed.

First of all, you may be asking yourself “What the heck is a heat-pump?” The most simple explanation, it’s an air conditioner that can work in reverse to also heat a house. The ‘mini-split’ or ‘ductless’ part of it is designed for a home that doesn’t already have heating ducts plumbed to distribute air, like mine. There’s an outdoor compressor/condenser and an indoor, wall mounted air handler. Then between the two units are two small refrigerant lines. Since there are no duct losses, it can be a very, very efficient way to heat a home. For more info on the advantages and disadvantages, the DOE has a nice writeup on mini-split heat pumps. The system is based on the principal of capturing and moving heat around, vs. generating heat from burning something (like a gas furnace) or heating up elements with electricity. Since Western Washington State is a moderate climate, this should be one of the most efficient and cost effective methods to both heat & cool my house.

At first my wife thought it was another one of my gadget geek ways, and didn’t see much benefit of having an air conditioner. Luckily for us, the system was installed a week before this summer’s record breaking heatwave (103* in Seattle) hit our area. We suddenly became our friend’s favorite place to come visit. The inside airhandler (image, right) is fairly smart looking, with a mirrored face. In fact, most people don’t even notice it’s there. When activated, a vent door opens to the bottom and it’ll blow warm air throughout the room. Since our house is fairly small and open, we figure the one air handler will do the job. In larger homes, you can have separate air handlers installed across the house, and they’ll all run on a single outdoor unit.  The air intake is situated on the top. Typically the indoor units are placed up high, so the air can more easily circulate in the room/house. Behind the wall, a condensate drip line has to drain to an exterior wall or drain, because the cooling action of the unit will cause humid air to condensate into water. Here’s the vital stats of our system:

• Model: LG Art Cool
• Capacity: 12,000 btu heating, 8,000 btu cooling
• List price: $1,300 without install and accessories. Expect to pay ~$5,000.
• Provides air filtration & ‘plasma’ ion air cleaner (great for removing odors)

So far the unit has been great for both heating and cooling. Both the indoor and outdoor units are exceptionally quiet. You’d be hard pressed to hear the inside unit during normal operation even from 5 feet away. The outdoor unit is also much more quiet than other A/C compressors I’ve heard. Even when operating under max cooling, I measured (using a TED 1000) only ~1,200 watts. Typically it’ll cycle between 400 and 1,200 watts in cooling mode. So far, going into the fall, I’ve seen similar results for the heating cycles. For comparisons sake, baseboard electric consumes 250 watts per foot of element. Our house has about 35 feet of baseboard element. When they’re all operating, they consume nearly 9,000 watts.

Over the summer, it did *raise* our consumption by 100 kWh (roughly $7) per month, since we never had A/C before, but I anticipate it’ll dramatically reduce our heating bills come winter.

An Interesting Note

After installation, I discovered the reason why our utility was offering such a large rebate. They wanted test cases. The major utilities across the Northwest are currently testing and extensively monitoring a couple hundred of these newly installed systems over the next year. They asked me if I wanted to be a part of the study, and gladly accepted (as long as I could view the data collected from my site). PSE sent out the energy consultant (Ecotope) to do an onsite energy audit, blower door test, and to wire up their instruments.

It’s curious to live in a large science experiment. As part of their monitoring, they’ve installed sensors on each of my circuits, temperature sensors on the exterior, air handler intake, exhaust, along with temp sensors on the refrigerant lines and an air flow meter on the top of the air handler (picture, left). Their main goal is to see the unit’s real world coefficient of performance, and how much energy it’ll save the household. They did a nice job of hiding the gear, but it’s everywhere and transmits via cell network every few seconds. Pretty cool, and I’m sure expensive stuff. I haven’t had the opportunity to use their data to compare it with what my readings show. From talking with their installer, the mini-split units they’ve examined work most efficiently when running on only 20-30% load, with a COP of 4+. As a comparison, baseboard electric has an approximate COP of 1. They said, even on the coldest day in Idaho, they saw an average COP of 2 from the heat pump system, which means even at its worst, the new heater will still be twice as efficient as baseboard. At its best, it’ll be 4-5 times more efficient.

I figure, with both the tax credit and incentives available, I should see a 5 year return on my investment, saving me $700 annually on my electric bill and cutting my heating costs by 60-75%.

Next major improvement in Nov-Dec: Heat Pump water heater. Cut water heating loads by 60%. That, combined with my mini-split heat pump, should bring my home’s daily energy usage to ~15 kWh ($1.20) a day – which is pretty impressive, considering I have a home server running most all day and an energy hog plasma screen TV. If I can get my consumption down to 12 kWh a day, a 3.5 kw solar array would cover nearly all of my annual electrical needs, effectively making my house a net-zero home.

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