Lesson -1: Principles of Eco-Design(Part Two)

2.Thermal mass:

• configure thermal mass to absorb sunlight-concrete, concrete masonry units (CMUs), brick, stone, and tile are typical materials used as thermal mass inside the building,the amount of glazing and insulation helps determine the amount of mass required to keep the house from overheating during the day and reduces the backup heat required during the night;

-thermal mass that is directly irradiated is much more effective than thermal mass that receives only reflected light,thermal mass requires that solar geometry be used as a design criterion for the placement of the mass;

-everything inside the house contributes to its thermal mass according to its capacity to absorb and store heat, known as its 'thermal capacity',the best materials for storing heat are those that are very dense, heat up slowly, and then give out that heat gradually: brick, concrete and stone have a high thermal capacity and are the main contributors to the thermal mass of a house, water has a very high thermal capacity, so it is well suited to central heating systems, air has a very low thermal capacity- it warms up fast but cannot stay warm for long, only when the walls and floors in a building have warmed up will the air stay warm.

• determine apropiate overhangs for all south glass
• limit east, west, and north glass while providing for cross-ventilation

-east and west windows lose as much heat as they gain, they are particularly problematic in regions with hot summers because they face the low solar angles in the mornings and afternoons,but they also provide an important function in creating cross-ventilation in rooms or for the entire house,also the  glazing becomes an important architectural feature, so the type of glass is important when placing east-west windows as the low solar heat gain glass can reduce the potential  overheating;

• design apropiate shading strategies for east and west glass

-the easiest way to limit summer heat gain through east and west windows is through strategic planting outside, trees and bushes that leaf out in summer and drop their leaves in fall provide for light and ventilation while shading the window when it is hottest outside,also you need to be  careful that the species selected doesn't grow too tall and lose its lower branches, thereby reducing its shading potential;

• calculate the backup cooling and heating required

-in a house insulated to current codes, thoughtful passive solar design can reduce the cost of heating and cooling by as much as 50%,in a superinsulated house, passive solar can replace even more fossil fuel than that, good design is the key, overheating is one of the main reasons that builders are skeptical of passive solar,there are some design softwares that can be  adjusted to take into account the passive solar contribution before sizing HVAC equipment. 

• insulate the house-insulating and air sealing the house are the perfect context for passive solar heating,when correctly installed with air sealing each type of insulation can deliver confort and lower bills during the hottest and coldest times of the year.

                    Eco-buildings are usually designed to have a high thermal mass for several reasons:

1. To hold over daytime solar gain for night time heating. A high thermal mass balances out the fluctuations in temperature that come from solar gain, soaking the extra daytime heat into the body of the building and releasing it slowly at night. The flywheel effect is most pronounced when the suns rays hit a wall or floor with high thermal capacity. For this reason eco-buildings are often designed with a dark coloured solid masonry wall and solid floor behind South facing windows.

2. To keep houses cool during the day in summer. A high thermal mass will reduce fluctuations in internal temperature during the summer. If a house has good ventilation during the night, its thermal mass can be cooled and it can then maintain that cool interior through the heat of the following day. In the extreme case of desert regions where daily temperatures can vary by up to 40°, traditional houses are usually designed to have extremely thick walls to moderate the internal temperature.

3. Increase the efficiency of a central heating boiler. A high thermal mass favours small boilers working at maximum efficiency, slowly and steadily raising the temperature of the building and then turning themselves off for sustained periods. Buildings with a low thermal mass, by comparison, tend to have much wider fluctations in temperature, and the boiler is constantly switching on and off to compensate.

To be continued...