Archive for the ‘Solar’ Category

More data on solar air heater

December 12, 2013

The recent cold snap let me collect some interesting new data. Previously I had reported on temperatures in the building with the solar heat on and off, but that didn’t tell how much energy was being captured by the collector. At the end of that post I speculated on a way to approximate measuring the energy.

Each day during the cold snap I read the power meter at 10:30pm. The Weather Depot website gave me the Heating Degree Days for each day. (Heating Degree Day is the indoor temperature minus average outdoor temperature; a measure of how much heating is needed. Colder days have more HDDs.)

This gave me a table, and I could calculate a ratio HDD/KWH which should be a constant

HDD (55F indoor) KWH/day Ratio
52 62.44 0.839
42 51.32 0.824
33 39.75 0.825

The ratio lets me predict, knowing the HDDs, how much energy the building would use.

I turned the solar on Wed, and collected data. It was a fairly clear day, high haze but strong shadows. If the solar is effective it should save me energy, ie, reduce the KWH that would be expected to be used for a given number of HDD

It Worked!  The Solar heater came on for 4-5 hours. While I never saw the temperature inside rise above the 55F thermostat setting, I used 6 KWH fewer than the HDD on Wednesday would predict.

6 KWH is 22% savings – about 1/4 of the energy, which roughly agrees with the collector operating for 1/4 of the day. The building has no thermal storage, its like a greenhouse that warms up in the sun and cools again when the sun sets.

The water heater portion of the system is the way I will store energy. I hope to do a final system leak test on that system this Saturday.

First data from solar air heater

November 30, 2013

I have been making (slow) steady progress on the “Cookhouse” project. The utilities got installed over the summer by some great contractors: Nolan Heating, Jeff’s Electric, Don’s Plumbing, Jamin at Energylock for the spray foam insulation and Tom at Avista for the new transformer. I spent Sept-Nov working outside on the siding which caused me to need to get the solar air and water heaters finished up enough to put the glazing on.

collectors on the south wall. Air heater is the set of tubes at the top, water heater is below

collectors on the south wall. Air heater is the set of tubes at the top (above the scaffold deck), water heater is below (click to enlarge)

I built two things into one collector. The lower 12 feet is hot water (pre-)heating. But having watched the sun angles I realized that there were 5 feet above that which get winter but not summer sun. I made an air heater in that area. I suspect the air heating gets some heat rising from the water heater — I didn’t seal them off from one another.

The hot water system is inspired by this design and will be the subject of another post.

For the air heating, I did a variation on the “solar can heater”  I used pre-made ducts rather than messing with a bunch of cans. I have a fan that draws air from the upstairs ceiling, thru the collector, and blows near the floor downstairs (opposite flow from the illustration).

To control the hot air system, I installed two conventional thermostats. One is typical house heating thermostat (on when cold) and the other is an attic fan controller (on when hot). The combination (hot in the collector, cold in the house) turns the fan on.

When the electric and heating was turned on I hooked up the solar air heater. In late October I measured 172F in the collector, 60F air going in upstairs and 122F air coming out downstairs.

indoor and outdoor temps for experimental and control days

indoor and outdoor temps for experimental and control days (click to enlarge)

Last week I was able to do some more systematic data collection on two sunny days with similar outdoor conditions. Nov 21 was the experimental day, Nov 22 the control. What I found was that the heater can warm the downstairs by 10+ degrees F over the warming I get without the heater (just the sun in the windows and warming the south wall).

I need to get some better instrumentation to take more data, but that will have to wait for another post.


Footnote. I have been mulling over how to get a better measure than these temperature data, what I want is units of energy. Since the only energy use in the building now is heating, I can read the meter for KWH in a 24 hour period. I just found this site where you can get heating degree days (1 degree-day = 1 degree difference in temperature for 24 hours). Even better, you can control the indoor reference temperature.

SO, if I turn the solar off and pick a cloudy day, I have a measure of KWH/day and a measure of delta-T/day which will let me estimate the building overall R-value/day. I think I can use that estimate of R-value along with the KWH & degree-day for a sunny day to estimate the energy gathered by the solar system.

UPDATE 12/29

I made 2 of these manifolds to fit 9 3" duct. Duct material is 5 foot. Backing is 1.5" of TuffR rigid insulation painted black. Once installed the pipes were sealed in with spray foam.

I made 2 of these manifolds to fit 9 3″ duct. Duct material is 5 foot. Backing is 1.5″ of TuffR rigid insulation painted black. Once installed the pipes were sealed in with spray foam.


Inside view upstairs. Hole at top is air going out to collector. Light comes in because collector not installed. 4" duct below goes downstairs where fan draws air down.

Inside view upstairs. Hole at top is air going out to collector. Light comes in because collector not installed. 4″ duct below goes downstairs where fan draws air down.

This is a conventional attic fan thermostat (on when hot) set at 90F. This (plus indoor temp) decide when fan comes on to draw air thru heater.

This is a conventional attic fan thermostat (on when hot) set at 90F. This (plus indoor temp) decide when fan comes on to draw air thru heater.

New Year’s Resolution: Reducing my carbon footprint

January 3, 2012

Making my Resolution was pretty easy, figuring out how to implement and assess it, not so much.

I’ve been doing a bit of reading over the holidays, Bernstein’s Aquaponic Gardening, Coleman’s The Winter Harvest Handbook: Year Round Vegetable Production Using Deep Organic Techniques and Unheated Greenhouses and some of the blogsphere including Roberts’ Brutal Logic posts here  and here as well as some discussion about the “marketing” of climate change with scare tactics like Roberts vs. a gentler approach to reach the electorate, see two sides here and here.  I’ve also glanced into some alternate perspectives including Worstall at Forbes arguing that delay in addressing climate change can save money (I think his logic is faulty). Also supporting the go-slow path a friend recently wrote me “But considering that 50% of American’s make less then $26,000 a year [what with] buying food and paying rent…well there isn’t money for those high end [climate saving] purchases. You can’t squeeze blood out of a turnip.”

I’ve got my monthly utility bills from Avista for gas and electricity in 2010 and 2011 which gives me some baseline. Avista’s electricity comes from a mix of fuels, including coal, gas and nuclear. They give information that should let me adjust my KWH to the fraction that is carbon-based. I don’t have records of gallons of gasoline purchased. My house is heated with wood, which raises some different issues about pollution and I have no handle on the amount of wood I use or its carbon content. And then there is the issue of adjusting my use of heating energy to account for the weather in the 2011 and 2012 heating seasons. Avista gives degree days in its bills but with a wood stove, there are days when you just don’t heat because you are not around to stoke the stove.

So, I am going to make my Resolution more specific:

Regarding gasoline – I will track how many miles I drive and how much gas I use and return to this challenge in 2013.  I put log books in each vehicle to begin tracking miles and gallons purchased. I can use these logs to also record gas purchases for lawnmower, chain saw and the like.

I previously challenged myself to buy only one tank of gas a month, but that challenge is complicated by having multiple vehicles and by using the in-laws’ vehicles at times. To give me something I can assess for 2012, I will aim to buy no more that 150 gallons of gas for the white car and blue truck I drive and for my various gas powered tools. Bicycling around Moscow has shaved my waistline, this is a path to continue.

Regarding electricity and natural gas – Last January I was thinking about these issues in terms of “buy local” and how to shift my purchases from Avista to spending locally. I have experimented enough with a clothesline in the greenhouse that I can see some reduction in electricity use. I need to build on this effort to reduce our footprint with Avista.

Sharon Cousins has advocated solar ovens enough to get me to try one and to build one, but I’ve not lived with them enough to make any claims that I am substituting solar energy for Avista energy. This is a path to continue. I’ve played with a mud oven and retained heat cooking, again not enough to make any claims about substituting wood as my baking fuel. Recently I found a hybrid idea, retained heat solar oven. Something to explore designing into the shared use commercial kitchen I am building.

In the Peterson Barn Guesthouse, my next steps are probably to use solar to supplement space heating and in our house, I’m working on pre-heating our hot water with solar. Both projects are low budget, a fan and ducting to blow excess warm air from the greenhouse and a homebrew rooftop solar collector.







Building my first solar oven

October 1, 2011

I celebrated the Fall Equinox by building and testing my first solar oven. One of those projects I’d been thinking about all summer and the waning sun motivated.

It was a project made of scraps. I had the plywood box from a WSU Auction. The 1/2 inch reflective insulation was left from building garage doors on Peterson Barn Guesthouse. It took a little practice to recover my (ca. High School) glass cutting skills, but they allowed me to re-use a piece of glass from a defunct cold frame.

The lid still needs a reflective treatment and a means to prop it at an angle to reflect into the box. As it was, I got 3 cups of beans and water to 135F from 11AM till 3PM. Needed another hour simmering on the stove to finish cooking them.

I needed to rotate the box to track the sun. To reduce that need, I want to think about wings that will bounce light from the side — ultimately having a bit of a light funnel.

Building a solar water heater

December 5, 2010

As part of a needed re-roof of my cold cellar I decided to build a place for a solar hot water collector. The idea is to site build the collector using copper pipe with fins attached. The system will be a drain back (that is a pump will run when the temp in the collector is high enough. If the temp falls, or the power fails, the pump stops and the fluid drains out of the collector, protecting it from freezing.) Ideally I will use a solar panel to power the pump.

2x6 framing for DIY solar panel

Also, the working fluid in the system is isolated from the city water (good because we have hard water that could lead to buildup in the collector) This means I need a heat exchanger between the solar panel and an old 50 gallon conventional hot water heater that I will use as storage.

The collector sits on the surface of a monitor built on the cold cellar roof. The monitor gives me both a north facing skylight in the cold cellar and a way to bring the pipes from the collector directly indoors for ease of access and protection from the elements.

Next steps are to finish the remodel and re-organization inside the cold cellar and then start making the insulated cabinet for the HW tank (cold cellar is unheated and cold, but never freezing).