Due to the recent spike in energy prices and the potential for this trend
to continue, it has become increasing necessary for laboratory buildings to
consider all available energy conservation tactics. Labs are notorious energy
consumptive machines, often requiring several times the energy per ft2 of a
typical office building. Other than the large volume of fresh air required
in a laboratory facility to sweep chemicals from the air, the second greatest
energy consumer is the removal of the heat build-up from equipment, occupant
loads, and solar gain. As a result, most laboratory facilities are cooling-driven
buildings.
Fig. 1. At mid-day in summer, solar energy has little opportunity to penetrate through building cladding. Roofing material has a greater potential for mitigating heat gain. All diagrams: David S. Brownlee/Perkins + Will.
Fueled by the computer-aided research breakthroughs in the past 20 years, lab
equipment loads have continued to accelerate. Facilities can help mitigate this
accumulation by reducing solar gain. For greenfield facilities (those on fairly
expansive open sites), this begins with the proper siting of the building to
take advantage of the natural environment.
Siting and landscaping principles
Proper siting includes several
strategies that will greatly reduce the heat load, or assist in dissipating the
heat load, of a building. Each of these strategies must be evaluated with the
local climate to determine appropriateness. Several of these solutions add no
cost to the facility, and in some instances, our firm has used them to help reduce
the first costs as well as the operating cost.
Orientation. Exploiting principles of building orientation is usually the
first line of attack. During summer, the sun rises to a very steep angle in
the middle of the day. At this time, solar gain through the façade is
less of a concern than through the roof system. Fig. 1 illustrates the
angle of the sun and the relative impact on the facility for a noon condition.
From this diagram it is easy to see that the solar radiation does not penetrate
deep into the building and has less potential of increasing the heat load in
the facility. It is also the most effective time of the day to attempt to use
solar shading to further reduce the heat gain.
Fig. 2 illustrates the angle of the sun in the morning and evening
conditions. During this period of the day the sun is at a low angle relative
to the façade of the building and has a far greater reach into the facility.
The sun’s reach into the building and the concentration of the solar
gain on the façade adds significantly to the cooling requirements of
the building. Typically the ideal solution is to orient the building along
an east-west axis with the longest side facing south or southeast, thereby
reducing the exposure of the façade to the morning and evening solar
gain.
Placement of the facility on the available site is only part of creating a
favorble “microenvironment.” The intellligent use of landscaping
features—both new and existing, if applicable—can yield great rewards
in energy savings.
Fig. 2. In morning and afternoon, again in summer, solar energy has a far greater reach into the facility. Orientation, glazing, and cladding can all be planned to maximize natural daylight without producing an unacceptable heat load.
Existing shade. Using existing shading features on a site can be an effective
method of reducing heat load on a building. The most obvious method is the
use of shade from existing mature trees to provide morning or afternoon shade.
Mature trees typically need to be close to the building to effectively provide
shading. The initial layout and orientation of the building should identify
trees on the site which could potentially provide shading. Grading of the site
must be designed to either keep the building near the elevation of the trees
to be saved, or lower the building below the trees through the use of retaining
walls. Fig. 3 gives an example of this.
Wind harvesting. In extreme climates we have oriented buildings to take advantage
of the prevailing winds on the site. Fig. 4 illustrates the principles
of wind harvesting. In this situation, we have placed trees between the prevailing
breeze and the building. The evapotranspiration from the trees cools the air
as it approaches the building. The cooler air moves over the building, removing
heat from the building mass. To further increase the flow of air across the
structure, we have placed parking or a non-landscaped zone on the leeward side
of the building. This non-landscaped zone provides a negative pressure lifting
effect as the heat rises off the surface, further accelerating the prevailing
wind toward the building.
Thermal harvesting. Thermal harvesting is similar to wind harvesting. In
this situation you take advantage of the temperature differential between hilltops
and valleys. By placing the building in the valley you are not only locating
it in a cooler zone, you are also taking advantage of the funneling effect
of cooler air. Cooler air tends to sink to the lowest area on a site. In a
valley location this cooler air funnels past the building, helping to cool
the building mass.
Fig. 3. If available on the site, mature trees can play a key role in reducing heat gain from solar energy. Careful grading may be necessary to ensure that the trees are used to maximum advantage.
Building envelope. The envelope of a laboratory facility should also be evaluated
from the aspect of a cooling-driven building. It is typically advantageous
to ensure the building envelope will assist in reducing the heat load. Aspects
of the building envelope to consider include the roofing, insulation, glazing
systems, and cladding.
Roofing. The roof of a lab building has tremendous potential to aid in reducing
energy consumption. Typically the roof is flat to accommodate air-handling
equipment and exhaust systems. Traditionally these roofs were covered with
black rubber-based products, which tend to absorb heat and increase the cooling
load. Instead, consider a reflective product with a high albedo factor, designed
to reduce solar gain. This is a very cost-effective technique that can significantly
reduce the cooling load.
When the goal is to remove heat, another method, which also reduces first cost,
is to reduce the insulation on the roof to the code minimum. As mentioned before,
the goal is the get heat out of these buildings. Adding extra insulation to
the roof will have the opposite effect. By reducing the insulation to the code
minimum, you allow heat to escape.
Glazing systems. Windows or glazing systems lose and gain heat by conduction,
radiation, and leakage of air. Heat transfer from the outside to the inside
only adds to the cooling load. Windows conduct heat through the glass and the
frame. Commonly used efficient glazing systems consist of multiple-glazed panes
filled with a low-conductive gas such as argon or krypton. Additionally windows
should be specified with thermally resistant window frames and edge spaces
to reduce the conductivity.
Radiant transfer allows heat to move from a warmer body to a cooler body. An
example of radiant transfer is when the sun shines through glass and into the
interior of the building. For glazing that will receive radiant heat, we recommend
low-E coated glass. Low-E coated glass has a transparent metallic oxide material
applied, which is able to reflect up to 90% of long-wavelength heat energy.
This glass blocks the heat-producing wavelength while allowing the shorter
wavelength of visible light to penetrate. The appearance of low-E glass is
similar to that of standard glass, but it costs more. To help reduce the up-front
expense, you might consider placing the glass only on the façades that
will receive radiant heating. We have further refined this strategy to stratify
the glazing on each floor by placing the lowest-E rated glass on upper portions
of the window section.
Air leakage through the window seals and frame edges creates additional cooling
system loads. Frequently the most dramatic increase of the cooling load is
the energy required to dehumidify the air to laboratory standards. The most
useful strategies for protecting against this issue are to specify low-leakage
windows and to inspect the installation of the windows.
Fig. 4. A “weather harvesting” plan for a lab building includes creating a landscaped zone on the windward side of the facility to cool prevailing winds, and a nonlandscaped zone on the leeward side to boost the flow of cooled air across the structure.
Cladding. After heat gain through windows, the second greatest contributor
to energy consumption from the structure of a building is through the cladding
system. The No. 1 culprit in wasted energy through cladding is typically unintentional
air leaks in the exterior envelope. Air leaks can be greatly reduced by proper
design and vigilance in inspection during construction.
Air leaks in the building envelope can create a significant problem for labs.
Each small leak leads to an increase in the cooling load and, as mentioned
in the glazing discussion, can significantly increase the energy required to
dehumidify the building. In addition these air leaks can effect balancing of
the HVAC system, reduce indoor air quality, and create drafts. The most common
locations for air leaks are from joints between the roof and wall; floor and
wall; wall and window; wall and soffit; and wall and foundation. Junctions
of dissimilar materials can also be a spot where leakage is likely.
In addition to proper design and construction observation, the following materials
are recommended jointing materials to reduce air leaks in the cladding system:
sealants (caulking materials, mastics, and coatings); weather-stripping (gaskets);
foams (polyurethane); and membranes (sheet and liquid-applied).
Often, the discussion of sustainability for lab buildings begins with the HVAC
system. This is natural since labs are such huge consumers of power. But ending
the discussion at that point ignores many other options for making the building
efficient. Make sure your “green” design considers the totality
of the project, including the important issues of siting, landscaping, and
envelope.
David S. Brownlee is the director of Science+Technology at Perkins+Will, Research
Triangle Park, N.C. (www.perkinswill.com). This article is expanded from a
version that appeared in the 2005 Laboratory Design Handbook (Nov. 2004), a
supplement to R&D Magazine and Laboratory Design newsletter.
