Background

Background

Heat Loss in Buildings

Figure 1. In class demonstration of basic wall heat values

Heat travels from cold areas to warm areas. In a building, effective materials are needed to slow down the movement of heat from inside the building to outside during colder weather. This reduces the heat load on the HVAC unit needed to warm the whole building. 

Heat is lost through two ways. As seen by the overall heat required from the heater system, the overall heat loss is dependent on conduction (Qcond) and convection (Qair). The heat lost from cold air traveling over surfaces will not be changed in this design project. Therefore, the heat loss from the building will be mainly dependent on the heat travelling through the envelope.

Equation 1. Total heat required by heater

The heat lost through conduction is dependent on the sums of wall area and U-values for the wall. The U-value is the inverse sum of R values for given envelope materials. The U-value represents the thermal conductivity of the envelope, which is desired to be low to prevent heat from escaping easily. Therefore, envelope materials must be large enough to have an efficient U-value. This saves energy by needing the heater to generate less heat to replace heat loss from the building.

Water Collection

Rainwater can be collected from non-permeable surfaces such as roof tops of homes. By researching average rainfall values per month in a given location, and determining the square area of the surface, the potential value of rainwater collected can be calculated. This collection of rainwater can be used as gray water in appliances such as washing machines, flushing toilets, and irrigation systems. By diverting water usage for those appliances to gray water, it reduces the amount of purified city water needed.

Figure II. Diagram generally representing a system of rainwater collection

Determining the amount of rainwater collected consists of multiplying the average monthly value by the non-permeable surface area in that same unit. The water collected is initially filtered and is held in a large storage tank underneath the ground. Piping, separate from the city water piping, carries the stored water to the appliances that are able to use gray water. This requires a separate plumbing system.

Solar Energy

Solar energy is generated by utilizing solar photovoltaic (PV) cells in order to absorb the sun's energy and convert it to usable electricity. The amount of electricity generated is dependent of the efficiency of the system, the area of the system, and the amount of solar radiation the system receives. Typically, these systems do not use batteries. This means that any excess power will be sold back into the power grid while any extra power required will be drawn from the power grid.

Figure III. Diagram generally representing a basic PV system in a home