Topics from the Power Line: Many decisions involved in HVAC design

Editor's note: The Energy Services Bulletin features real answers to real questions posed to our staff at the Energy Services Power Line. We hope you find it useful.

Question:

A Colorado community is building six new elementary schools, using a prototypical design. They want to consider innovative HVAC design options. For the first time, air conditioning will be part of the system, but the system will need to be operated with existing staff. The system has to be simple (low-tech maintenance) and energy efficient. What should they consider?

Answer:

The terms "innovative" and "low-tech maintenance" can seem contradictory, but innovative can mean combining simple technologies for enhanced benefit. For instance, ducting building exhaust and fresh air intake through a heat recovery heat exchanger reduces heating and cooling costs, but requires only simple cleaning.

Choosing the right system

Building energy management systems can be very user friendly if they are carefully planned out. Selecting the type of HVAC system is probably the most difficult decision to make, and depends heavily on the experience level of maintenance staff. Many school districts prefer to stick with HVAC systems they have used in the past, because they are familiar with troubleshooting and maintenance procedures.

The four-pipe fan coil systems, with central mechanical rooms for the boiler and chiller, are the choice of many school districts—most of the system's maintenance is on fans, pumps and filter change-outs. Ingenuity is needed in arranging equipment for easy maintenance and noise control.

Other school districts have gone with individual heating and cooling units for each classroom, with self-contained modules that can be removed and taken to a central repair shop. Neither of these approaches requires a high level of maintenance inside the building, and chiller and air-conditioner maintenance can even be contracted out.

Standardized central fan variable-air-volume systems, which supply varying amounts of heated or cooled air to satisfy temperature and fresh air needs are in use in some school districts. This system is more complicated to maintain on a daily basis.

A number of newer technologies being used in schools include ground source heat pumps, thermal storage and gas-driven chillers. Life-cycle cost analysis is the main method for deciding which system to use.

Don't skimp on maintenance

The adage "penny wise and pound foolish" too frequently applies to maintenance schedules. Routine maintenance often gets shortchanged as funds are allocated to items that directly impact education. As a result, what is essentially preventative maintenance gets deferred, leading to indoor air quality (IAQ) problems or an emergency situation when the boiler or the heating system fails.

Dampers are the one component of the HVAC system that must be maintained.  Fresh air, exhaust and return air dampers must be routinely checked for proper operation. A building lacking outside air cannot properly dilute indoor contamination. An outside air damper on an air handling unit that does not open or modulates to the improper position may not allow enough outside air into the building.

Lack of adequate fresh air leads to IAQ problems, but too much outside air creates excess heating and cooling loads. Changing filters on a regular basis greatly reduces the dirt and contamination that enter HVAC system components and then the air stream.

Boilers that are serviced annually provide more efficient heat. HVAC piping (i.e., steam, condensate, hot and chilled water piping) contains high concentrations of corrosion inhibitors to extend its usable life. The proper amount of outside air is an important part of HVAC design. Because most damper controllers can go out of calibration every few months, the entire HVAC system's automatic temperature-control system should be checked and recalibrated as prescribed by the installing contractor. Testing, adjusting and balancing should be performed as an annual check on the entire system to ensure it is maintaining design flow rates and set points.

Balancing efficiency, air quality not easy

Getting good energy conservation and good IAQ in the same building may seem like conflicting, even mutually exclusive goals. This is one of the challenges for innovative designers—how to minimize energy consumption while maximizing IAQ. Finding that middle ground is now the Holy Grail for many HVAC manufacturers and designers, along with designing systems that are more easily accessible for cleaning and maintenance.

For leads on HVAC designers in your area that are innovative and work with schools, try contacting the Green Building Professionals Directory.

Resources

Green Building Professionals Directory

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