Green House on Watson

From the beginning of recorded human history people have sought shelter from wind, rain, and snow either in caves or in buildings which they have built for that purpose. In addition to shelter from the elements the buildings provide an opportunity to control the temperature and humidity of the air inside them. People are most comfortable when the temperature is around 70 F and the humidity is moderate. When the outside air is very cold, a furnace or some kind of a heat source inside the building can heat the inside air. When it is very hot outside, we try to control the flow of heat energy into the building and we may even cool the air with air-conditioning equipment. In either case the choice of building materials plays a critical role in our ability to maintain a comfortable temperature inside. The ground tends to remain cool, so caves, basements.... buildings built partially underground tend to be cool in those parts that are underground. Certain types of brick or clay change in temperature slowly and tend to "hold in" the heat. Walls of these materials might heat up during the day - soaking in heat from the sun and from the inside air, and cool down at night - radiating to the cold night sky and also radiating energy to the inside air. Thick walls of brick, clay, or stone often provide a cool daytime shelter and a warm night shelter in hot climates. Thinner walls made of wood planks will not have the same properties. Unless we add other materials to those walls it will usually be difficult to maintain a different temperature inside relative to the outside temperature.

Two ideas are important here. The first is the idea of thermal resistance. Heat energy flows from hot spaces to cold spaces and the rate at which this energy flows increases as the temperature difference increases. The material which separates the temperature extremes has a certain resistance to energy flow. When the resistance is high, the rate at which energy flows through the material is low; when the resistance is low, high energy flow rates are expected. We insulate walls to lower the rate at which energy flows through the walls. Insulation increases the thermal resistance or "R value" of the wall. As part of this exercise you will use the "R values" for the windows, walls, floor, and roof of a building to calculate the rate at which energy flows out of a building. Knowing the dimensions of the walls, windows, floor, and roof, you can calculate the rate at which energy must be supplied to the building (equal to the rate of energy flow out) in order to maintain a certain inside temperature. The second important idea is the idea of the heat capacity of the building materials. Heat capacity is a measure of a material's ability to store heat energy. Metals tend to have low heat capacities. When heat energy flows through a metal, it changes temperature quickly. On the other hand, stone or cement has a much higher heat capacity. When heat energy flow into stone it changes temperature very slowly and tends to "store" the heat energy. Passive solar homes usually include a large mass of stone, rock, or other material with a high heat capacity. This thermal mass will heat up during the day when the sun shines. At night when it is cooler, energy can be drawn from the thermal mass. It is interesting to note that water has a very high heat capacity. Open water inside a house might create humidity problems, but in our atmosphere, the heat capacity of water has a significant effect on moderating temperature and on the weather pattern in general. In the overall energy demand for a house the high heat capacity of water also means that it will take a lot of energy to change the temperature of water. Ground water or city water comes into a house at about 55?F; water heaters are typically set at 120-130?F. The water heating system must be carefully considered when designing a house with low energy demand.

When we talk about heating and cooling of buildings we are talking about energy usage. When energy was inexpensive and when we thought we had an endless supply of fossil fuels, we did not worry too much about energy conservation. Now that we realize that our fossil fuel resources are limited and that burning them carelessly has undesirable environmental consequences, we are more concerned about conservation and about renewable energy sources. Insulation in buildings reduces energy flow rates and reduces energy demand. If insulation can be made from materials which are normally thrown away then we can reduce landfill demand and also save energy. Paper is an excellent insulator and paper also currently accounts for over 34% of the volume in our landfills. Cellulose insulation is typically made from recycled paper.

Many other materials may not be appropriate as insulators but they may release a lot of energy when burned. Waste to Energy plants capture this energy and result in only a small volume of ash going into a landfill. Air quality in the burn process may be a concern, but research into the safe, clean burning of items such as tires and other trash is certainly worth looking into. Note that Grand Rapids has a Waste to Energy mass burn facility on Market Street and that there is a District Heating Plant on Fulton Street across from Van Andel Arena. The District Heating Plant has been in place for many years and steam is generally produced using natural gas burners however when market conditions are favorable, steam generated at the Waste to Energy plant is piped a little over a mile underground to the District Heating Plant. More than 80 buildings downtown (including GVSU's DeVos Center, the Van Andel Arena, and the Public Museum) are heated from the District Heating Plant.

Follow the link below to view the Heat Load calculation for the Green House on Watson. After reviewing the steps, select the link for the Excel spreadsheet and modify the inputs shown to determine the effectiveness of insulating an uninsulated home.