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Tips & Tricks
The Building Envelope
The building envelope consists of the walls, windows, doors, roof, floor and foundation. This exoskeleton does much more than simply contain the conditioned air for the comfort of the occupants. It is also a major contributor to the heating and cooling load. Heat moves through each of these elements, into the building in the summer and out of it in the winter. The higher the temperature difference the greater the flow of heat. The quantity of heat is also dependent on the quality of the insulation: better insulation increases the thermal resistance of the building envelope. Many projects focus on this principle of building design as a cheap, effective way to lower energy consumption.
- Instruct staff to lower blinds and close curtains in the summer
Windows have the lowest insulation value of any element of the building envelope. They also permit radiant energy to enter a space, as opposed to conduction through the walls and roof. Thermal radiation accounts for a large portion of the energy in natural sunlight. Closing curtains or blinds will reduce the radiant contribution of the light and also reduce the conduction of thermal energy through the window. An air space is created between the blinds and the window that, since air is an outstanding insulator, increases the resistance to heat flow. Double pane windows take advantage of this same premise by trapping an air pocket between the panes. This enhances thermal performance. In the heating season the opposite applies. Radiant energy entering through the windows will augment the space heating system.
Double paned windows with blinds are ideal for all seasons. The insulation is needed in all seasons to retard the heat flow out in the winter, and vice versa in the summer. The blinds can either block or enhance the flow of solar radiation.
- Make proper use of building vestibules
A vestibule is an elegant architectural feature of a building entrance that can also be a practical and effective energy saver. The double set of doors reduces a major portion of the building load attributed to the envelope: exfiltration and infiltration. These are, respectively, the passage of conditioned air out of the building and the movement of unconditioned air into the envelope. Busy building entrances can lose much energy, approaching losses from a door open to the exterior all the time.
The double set of vestibule doors greatly reduces the flow of air through an entrance. Automatic operation prevents a clear passage for air flow, since one set of doors is always closed. Also, the volume of air trapped between the portals acts as a buffer to the transfer of heat through the vestibule. When there is no traffic the trapped volume or air is an effective insulator that increases the thermal resistance of the passageway. Otherwise the glass vestibule can be a source of high energy loss.
- Kitchen conservation measures
The single most intensive user of electricity in an institutional facility, such as a school or hospital, is the kitchen. This is especially true of a kitchen in which most of the appliances are electric. An expensive but worthwhile project is to convert an all electric kitchen to gas appliances that are cleaner, more efficient and cheaper to operate.
Short of a major retrofit there are many routines the kitchen staff can follow to save energy. Cooking with lids on the pots and pans is a good start. If the lids are tight fitting they will hold some pressure in the container and the liquid within will boil sooner and with less energy. Using lids keeps steam from increasing the humidity in the kitchen. High humidity increases the latent load on the air conditioning, which is a significant portion of the total load on the HVAC equipment.
Another helpful procedure is to use exhaust hoods only when cooking. These hoods draw copious quantities of air from a room - many room volumes per hour. This is air that has already been tempered, and the energy spent doing so is lost when it is exhausted to the atmosphere.
Other policies will reduce the heat generated in the kitchen, and thus the energy needed to cool the space into the comfort zone. These include turning off food warmers when not in use, preheating the ovens for baked goods only and using microwaves for after hours cooking of small quantities. These procedures will not only cause less waste heat to be released into the air conditioned space but will lower the energy needed to do the cooking itself.
- Increase use of available daylighting
The ideal lighting for any visual activity is natural light. It is best for color rendition, and it is a boost to the attitude and performance of the people within a space. Artificial lighting can only approximate the real thing, and then only a narrow band from the whole spectrum. It is always prudent to make the most of available daylighting, since it is not only the most healthy but also the cheapest light source.
Few offices can get by on daylighting alone. A common compromise is the use of multiple level switching. The perimeter offices of a building with outside exposures can have some lamps in each fluorescent ceiling fixture on one switch and the balance on another. For three lamp fixtures this permits four levels of lighting (off, one, two and three lamps) that can be used to supplement the available daylight. In large open offices, exterior hallways or classrooms with perimeter daylighting the outermost row of lights can be switched separately, or turned on by a photocell when the daylight is inadequate. The small additional initial installation cost will be compensated many times over by the savings and the occupant's comfort.
- Increase insulation thickness if it is less than R-10
Older buildings were designed at a time when energy was inexpensive and it was not economical to provide an effective amount of insulation. A good portion of the envelope losses are through the ceiling and the floor of a building if it not slab on grade. These areas are usually accessible and it is easy to increase the amount of insulation. Areas with colder winters and hotter summers should strive for at least R-10 insulation. A practical way to determine the ideal quantity of insulation is to survey local contractors to determine what they install in new buildings.
- Install shading devices on south & west facing windows
The highest heat gain of buildings in the northern hemisphere is from the south and west exposures. The energy consumption profile is reduced when windows facing these directions are shaded. Internal shading with curtains or blinds is one method, external shades are another. The application of solar film on the windows is also effective. The solar film has the benefit of reducing the radiation component of the glass - thus a big portion of the heat gain - without blocking the light that is itself often an energy saver. A final solution is solar screens for he south and west windows.
- Plan landscape shading with fast growing trees
The critical exposures of a building in the northern hemisphere are those facing south and west. They receive the most direct sunlight in the summer and account for a majority of the building's heating load. Shading of windows with blinds or awnings will reduce this heat gain somewhat, but trees will do this and more: they can shade the walls and even the roof of small structures. Deciduous trees, in addition, will lose their leaves in the winter to expose the building to the warming sunlight.
Landscaping has another benefit. A portion of the heat striking the lower walls of a building arrives indirectly, reflected from rocks, sidewalks and parking lots or re-radiated from these surfaces. Shrubs, grass and ground cover reduce this heat gain by blocking the heat transfer path or dissipating the thermal flow. Shrubs are quite effective if they shed their leaves in the winter or can be trimmed to open the thermal path to the south and west facing building walls.
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