HVAC SYSTEMS

Proper HVAC design is crucial to achieving an environmentally responsive sustainable design. Not only do HVAC systems offer great potential for energy conservation, they help ensure that the indoor environment is healthy and safe.

The surest way to achieve good indoor air quality is to control the materials used in the finished construction, which is part of the HVAC engineer's expanded proactive role, and to improve filtration in every component of the system. That includes the filtration of outside air for the guestroom primary air system, all of the public- and back-of-the-house-area units, and, especially, the guestroom units. Source control of contaminants is vital and a joint-team effort. The use of low-volatile-organic-compound materials, the avoidance of formaldehydes, and the reduction of the off-gassing of trace contaminants from interior-finish materials immediately improves indoor air quality, lessening the burden on the mechanical systems.

Filtration.

Traditionally, filtration in hotels has been minimal, especially in guestrooms, where filters generally are coarse throwaway units. These have proven to be less than satisfactory in arresting many of the smaller particles found in the guestroom return-air stream. Ineffective filters cause clogging of coils and drain pans and contribute to the development of biological growths. Improving filtration with mini-pleat filters in guestrooms and high-efficiency filters in other air-handling units begins the process of improved air quality; however, this can be effective only if the filters are inspected, maintained, and changed on a regular basis. Here again, the human component proves critical to maintaining the environmentally responsive hotel and reinforces the need to train and involve the entire staff.

Air temperature.

In traditional hotel HVAC design, the primary emphasis is on air quality and temperature control. Eco-hotels take a far wider view of the important requirements: A healthful environment is one in which humidity is carefully controlled, attention is paid to air motion and velocities, and the entire conditioned environment is delivered with low acoustical impact. While considered in conventional hotel design, these elements, especially acoustics, take on added importance in environmentally responsive designs. Many low-end hotel rooms utilize noisy packaged or unitary air-conditioning units that can have a significant negative impact on a healthful environment. To that end, control packages that keep the unit at low speed for as long as possible and variable-speed fan-coil units are popular.

Humidity.

Humidity control is especially important because it not only is critical to guest comfort, it prevents mold problems that destroy fabrics, carpets, and wall coverings in many tropical environments. Humidity is especially difficult to control during part-load periods, when cooling coils cycle off and lose their ability to remove moisture from the air flow. The guestroom-ventilation scheme must account for moisture control at all times, especially when cooling coils are off and ventilation air continues to be introduced. The most common solution involves introducing treated and dehumidified primary air continuously to each room. Desiccant equipment sometimes is used in very humid areas.

Controls.

Controls are an important component of environmentally responsive hotels. Not only are they at the heart of maintaining comfort, they are fundamental to energy-conservation efforts. Conditioning a space to a desired comfort level is important when the space is occupied. When it is unoccupied, allowing the comfort conditions to drift produces tangible energy savings. A number of manufacturers offer control packages that confirm occupancy and permit conservation.

Energy.

Energy conservation is not limited to controls. Operators of environmentally responsive hotels seek every opportunity to develop systems that take advantage of renewable energy resources. One such system, which will become more popular in the near future, is the geothermal water-source heat pump. Water heat pumps have been available for some time and have become a standard component in many guestroom designs. The current trend is toward the development of low-temperature geothermal units, especially ones that use environmentally friendly refrigerants. Vertical high-rise units using R-410a are in development and expected to be in operation next year. Units using R-407c will follow soon after.

Passive energy sources also are popular and very effective. For example, routing outside air through underground tunnels (or piping) tempers the air, cooling it during the summer and heating it during the winter. Although altering the temperature of air by a few degrees may not seem significant, the energy-conservation potential over the life of a hotel is enormous. In a similar manner, there are numerous ways to use the building as a "free" solar collector. One popular technique is mounting a dark curtain wall skin several inches from a solid facade on a sunny wall and simply drawing outside air behind the skin. This can effectively add several degrees of heating during the winter.

Solar energy is another renewable energy that grows more viable daily, as collector efficiencies improve and costs decrease. In environmentally responsive buildings, the use of batteries to store photovoltaic energy is problematic, as it introduces environmentally unfriendly lead and acid to the site. There is a need to develop real-time uses of solar energy, avoiding the cost and complexity of storage altogether.