A Harsh Winter for Solar

The past two winters may have been an ordeal for some, but for us they were something of an experiment. They gave us the opportunity to study the performance of our solar home under extremely harsh conditions. For example, in December, January and February of 1978-79 in Durango, Colorado, there were 21 nights when the temperature went below zero Fahrenheit. From November 26th through April 15th, the overnight low was above freezing only eight nights. There were 25 days in December and January when the high temperature for the day was below freezing. We received just over 130 inches of snow during the winter, with more than 70 of those inches falling in December and January. We received less than 60 per cent of the potentially available sunshine instead of the usual 70 to 80 per cent, according to my accounting. A harsh winter by Durango standards, indeed.

The 1979-80 was exceptionally cloudy and we got a lot of snow, but the temperatures were somewhat milder than in 1978-79, while the 1977-78 winter was clear and relatively mild.

How did our solar home perform under such conditions? Quite well, we think. Let's look at some of the construction details of the house, of its solar system, and then look at some of its performance figures. Because it was the most severe winter we have had since moving in the house, and thus a more severe test for the house, the performance data will be from the 1978-79 winter.

The house was designed to our specifications by a Durango architect, Brian Kesner, and built by a local contractor. It is a middle-class home. There are three bedrooms, two baths, a living room, kitchen, utility room, air-lock entry, food storage room, and a two-car garage. We heat the 1650-square-foot living area, but the air-lock entry, food storage room and garage are unheated. Since our daughter is away at college, the upstairs rooms, a bedroom and a bath, were fully heated only occasionally through the winter. Most of the time residual heat from the house is sufficient to keep the temperatures in the upstairs rooms in the 40 ' s at night. We cannot close this area off completely from the rest of the house, though we can and normally do close the doors to the rooms.

There are five key aspects to the home's winter comfort. The first is conservation. The house is heavily insulated; it is dug into a hillside to a depth of seven feet along the north wall on the first floor; there are no north windows on the main floor; the 2-by-6 perimeter walls permit five and one-half inches of cellulosic insulation in the walls, and, there are nine and one-half inches of cellulosic insulation in the ceiling. Conservation should be the first consideration in all homes, solar or not.

Second, the house uses passive or natural solar heat. Basically this means we have a lot of south-facing windows. The sun streams through these windows in the winter and heats the interior of the house. It is blocked from doing so in the summer by one half foot overhang. The house never needs any other heat than this passive heat on a clear winter day no matter what the outside temperature is! In fact, on even the coldest winter days, if the sky is clear, the house sometimes gets too warm.

Many times, following a sunny winter's day, our house goes through all or most all of a very cold night with no heat other than that which has been gained through our south-facing windows and stored in the walls, floors, and furniture. The house gains passive heat on most cloudy days, too. This passive heat is so effective we usually do not even turn on the furnace pilot light until sometime In November and we usually turn it off in April. We used essentially no active solar or natural gas heat in the house after mid-April the past three years, and we have used only a little electric heat occasionally in the bathroom in the mornings.

Third, we have an active solar heating system. This includes solar heat collecting panels which face approximately south. They were built locally by Jim Costello, a former college physics professor,, who is one of an enterprising group of solar enthusiasts organized as TRITEC Solar Industries. The panels use an invention by Wilfred Heyen and Keith Olinger of TRITEC called airHair (TM), which is essentially a large pad -- much like a large furnace filter -- spray-painted black. We have fifteen of these glass-covered panels, giving us a total of just over 250 square feet of effective collector surface. The collectors are vertical instead of the usual latitude-plus-15 angle commonly prescribed in the solar literature. We went with the vertical collectors for several reasons: easier to build, easier to keep clean and air-tight, and we only use the system for wintertime heating.

The active system also includes ducts to deliver cold air to the collectors and to take hot air from the collectors either to storage or to the house. In the utility room, there is an air-tight, heavily insulated eight-ton bin of rocks in which we store heat from the collectors for later use, giving us heat storage for one or two days of home use. There is an air handler -- a large box with a blower and dampers -- which forces and directs cooled air to the collectors and warm air to storage, directly to the house, or from storage to the house. An electronic "brain", also a TRITEC product, directs the actions of the system.

The "brain" operates on the basis of information received from a heat sensor In the rock bin., from the house thermostat and from a heat sensor located in one of the collectors. On the basis of the information received from these three sources, the brain can direct the system to do one of five things: 1) If the collectors are hot and the house is cold, hot air is directed from the collectors directly into the house. 2) If the collectors are hot and the house is warm enough., heat is sent from the collectors to the rock storage bin. 3) If the collectors are cold and the house is cold, heat is taken from the rock bin and directed into the house. 4) If collectors, house, and rock bin all are cold, a natural gas furnace is started and runs just like any other forced-air system. 5) Finally, if the collectors are cold and the house is warm, the system shuts down. The level of warmth for the house is fixed by setting the house thermostat. Once the thermostat is set, the system works automatically, as directed by the electronic "brain". The "brain" Is really a small computer.

We do, of course, have back-up heat. This is the fourth key aspect of the house. It is usually not economic to size a solar system to provide 100 per cent of a structure's heating needs. Our back-up is provided by a conventional gas forced-air furnace downstairs and electric heat in the upstairs bedroom and bath. We heat our domestic hot water with natural gas. This is because no local contractor could do a solar water system when we were designing the house. Hindsight tells us we definitely should have persevered and found someone to do a solar water heater because of the year-round energy savings and the short payback we could have realized. So much for hindsight.

The fifth key aspect of the house is the Mansfield family. We open and close drapes at the right time. We close off rooms which are not in use. We put up space-blankets on the windows on cold nights. We keep the bedroom slightly below 60 F, by preference,, in winter. And, if the house temperature falls a little below 65 F before bedtime, we put on sweaters instead of turning up the thermostat. In short, we work at saving energy. Our efforts are important in the overall performance of the house. A non-conserving family in the same house could experience far greater energy costs.

For the past three winters (November through April of each year) I have kept records of how the house has performed. These records include the amount of natural gas and electricity used, the temperature in the various rooms of the house, the solar storage temperatures, outside temperatures and general weather data. The information was recorded in the morning and late afternoon each day. In addition, I recorded the official high and low temperatures from the local newspaper each day. During the summer (May through October), I record only the amount of electricity and natural gas used and their cost.

Now to the performance figures: On the average, during the summer of 1978, we used 407 kilowatt hours of electricity and 1900 cubic feet of natural gas a month. Remember, we heat all of our domestic hot water, year-around, with natural gas.

This electric and natural gas energy cost us an average of $30.21 a month for that summer. These summer averages are necessary in determining the winter heating bills, because the winter heating is roughly the increase in usage over the summer average. This is an over-simplification since all the energy used in the house releases heat into the house, summer or winter.

Our total winter heating bill was less than $75-00! November 1, 1978, through April 30, 1979, was one of the worst winters in a long time locally, according to those who keep records of such things. We used an average of 463 kilowatt hours of electricity a month at an average monthly cost of $22.17. We used an average of 5900 cubic feet of natural gas a month at an average cost of $20.42. These add up to an average of $42.59 a month or only $12.38 a month above the summer average; in other words, $74.28 was our winter's heating bill.

This rosy picture is diminished by the fact that we have to pay for the solar system. The system cost $6,000 and increased our house payments by about $35.00 a month. This increase must be added in as a cost. Taking $35.00 times twelve months plus $12.38 times six months gives us an annual total cost of a little under $495 for heating and the solar system. We feel our solar home, even with the year-round system repayment costs, is more than economically competitive with homes using electric energy or propane gas for heat in our area. Solar probably does not compete with natural gas as an energy source, yet. But, it is close, and the way natural gas costs are going up, it won't be long before solar is competitive with natural gas.

All of these figures on our solar home add up to the fact that the house during the very harsh winter of 1978-79 did not use a great deal of gas and electricity over the summer averages. Its performance was even better during the 1977-78 and 1979-80 winters; these winters were not as severe as that of 1978-79.

The house is very energy efficient; it keeps us comfortable and there is definitely a good feeling about living in an energy conserving solar home.

In spite of the good performance of our present house, we plan to build another solar home. What will we do differently when we build another solar home? 1) We'll do an even better job of energy conservation. 2) We'll have more insulated mass in the floors and walls of the house to absorb the passive solar heat. This mass will keep the house from overheating on those clear winter days and will provide even more passive or natural heat at night. 3) And, we'll have an active solar system to heat our domestic hot water all through the year. We'd like to reduce the energy we use even more "than we have." We believe we can do so and remain comfortable in the process.