Notes from Windward: #62

Cook stoves, air quality and unintended consequences

The working heart of the new kitchen is a 4' wide commercial cook stove with a 2' wide grill and four large burners. It's currently set up to use propane, but we're planning on switching it over to hydrogen a couple of years down the road. More about that in the next article.

The gas supply to the stove is controlled by a normally closed solenoid valve; in order for fuel gas to flow through the valve, it has to be energized. If the power fails, then the value automatically closes and shuts off the gas. Our previous kitchen caught fire as a result of a power outage, so we're very sensitive to the need for fail safe systems in the kitchen.

The valve is controlled by three switches connected in series. The first is the master shut-down switch. Throw that switch and the gas is shut off right now.

The second switch is a timer switch. Assuming that the master switch is on, this switch allows the cook to turn on the gas for a set period of time, say for two hours. The switch has an internal timer mechanism which measures out the time and then shuts off the gas. This way the cook doesn't have to remember to turn off the gas when they're done with the stove - it happens automatically.

The third switch is a thermal switch located up in the hood. If the temperature in the hood exceeds the switch's setting, it trips and shuts off the gas supply to the stove.

This may come across as a considerable degree of "over kill," but when it comes to peace of mind, fail safe systems are a great investment. This far back in the woods, fire insurance isn't a viable option, so we strive to do whatever we can in the way of fire prevention.

In order for a system to be sustainable, it has to be efficient. One way we've enhanced the efficiency of the stove is by shutting off all the pilot lights, and using a piezo igniter to light the burners. Piezos use a crystal to generate a spark. When you press on the red button on the side of your bar-be-que grill, you're storing energy in a crystal by bending it. When the crystal snaps back into place, it emits a spark that ignites the flame.

In a commercial restaurant, where they're always in a rush and have to light a burner many times a day, the gas used by a pilot light that's always burning isn't significant. In our case, where the stove is primarily used for a few hours in the morning, and an hour or so in the evening, the gas used by three pilot lights running 24x7 involves a notable amount of gas needlessly consumed. Better for us to just light a flame when we want one.

While pilot lights certainly are "convenient," one of the warning signs you learn early on in the study of sustainability is that any time you hear a system touted as being "convenient," it deserves a second look, since convenience often comes at a high price in terms of sustainability. When we can get convenience through good design, that's great, but when it comes at the cost of lessened efficiency, that's not.

Sustainable design isn't just a matter of a system's cost efficiency; other factors, such as the impact of the system on the community's long term health also have to be taken into account. No where is that trade-off more apparent than in the matter of ventilation. Too much air exchange and you're wasting heat; too little, and the air quality inside the building can drop dramatically.

It's easy to "go on a mission" and close off every crack and opening that allows the warm air inside a building to escape. The problem is that this also prevents the refreshment of the inside air, something which is necessary in order to purge the various gases that can build up inside to the point where the quality of the inside air can become a problem.

The reason for sealing up a building is not to prevent the exchange of air, but rather to control it. Every bit of warm air that leaks out through an open is replaced by an equal amount of cold air leaking in somewhere else, a thermal loss which has to be made up in order to keep the building warm.

Since we're using a wood stove as our primary heat source in the kitchen, we have to be especially careful to insure that the air pressure inside the kitchen exceeds the external pressure, otherwise it's possible for the exhaust fan over the stove to suck air down the woodstove flue thereby introducing carbon monoxide into the living area.

For example, I recall one situation in which a family suffered from a series of difficult to diagnose health problems each winter. Eventually the problem was sorted out, but not until the family gone through a couple of miserable winters. The "problem" was that they had gone on an energy saving program involving replacing their old windows with new, high-efficiency vinyl ones, new doors with better seals, and a host of other steps all of which effectively shut off any air exchange between the outside and the inside.

The problem happened when they did laundry since the repairs they'd done had effectively blocked off usual paths by which outside air came into the house. When they ran the dryer, an internal fan exhausted the moist air to the outside, at the same time lowering the air pressure inside the house.

Since the usual leaks had been sealed, the path of least resistance for the outside air was to come down the stovepipe, through the wood stove and into the house. The unintended consequence was the introduction of carbon monoxide into the home environment, a condition which resulted in chronic health problems for the family.

There are obvious technological and economic challenges which have to be overcome in order to bring renewable/sustainable systems online, and most of those can be addressed beforehand. Still, no matter how carefully you plan, there will still be unintended consequences to cope with, and how quickly you figure out how to cope with them will often determine whether the system will work or not.

In this case, we're installing a special vent through the back of the stove in order to provide fresh air to the stove top area when the exhaust hood is running. This way the fresh air feed will not dilute the warm air in the room, and the wood stove won't be put into a reverse flow condition.

Solar lights on wintry nights

What we're going to do

Windward Home Page - - - - Notes From Windward, Volume 62