State-Of-The-Art Design And Technology Can Meet Both Energy And Comfort Demands
The CFC phaseout has forced facility executives to take a hard look at their HVAC systems. At the same time, current technology offers significant opportunities for energy savings from the heating and cooling system, typically the second-largest energy user in commercial facilities. On top of all that, the definition of comfort has evolved rapidly over the past decade.
At one time, HVAC systems satisfied the comfort issue by simply making sure the work area was warm or cool enough for most occupants. Now, comfort is being refined to include indoor air quality and outside air exchange.
All in all, it’s a tall order: The HVAC system is expected to achieve comfortable conditions for the individual and the masses in the office without harming the delicate global atmosphere. A good example is the CFC phaseout.
Facility executives have three choices: contain CFCs in existing chillers, convert existing units to alternative refrigerants or replace existing machines. Installing new high-efficiency equipment can result in significant energy savings.
Modern HVAC equipment offers improved efficiencies, which are being achieved with better motor performance and better temperature splits in the refrigerant tubes. Today’s HVAC systems also offer better part-load efficiencies than older models. Multi-stack units and horizontal screws run more efficiently at part-load levels than earlier models. The economizer bundles are better than they used to be, so the systems run more efficiently.
The recent improvements in chiller efficiencies are the result of refinements in many small places. Manufacturers have done it by better designed compressors, by improving heat transfers. Every component has been reengineered.
New materials, notably plastics, offer major potential for increased HVAC advances that end up benefiting building owners and managers. New materials make units more efficient, easier to install and more corrosion resistant. HVAC systems are becoming more component oriented so they can be put in after the building is built.
Resolving IAQ via HVAC
One of the biggest challenges facing facility managers today is how to meet ASHRAE’s current standard for outside air exchange. Variable air volume systems and normal applications need to be reexamined to meet ASHRAE fresh air standard.
To maintain energy efficiency and meet the new standard, multi-zone air-handling systems may need some overhauls. The normal unit has two decks — one for warm air and one for cool. Provided air is mostly being recirculated, the two decks work effectively.
With the larger temperature differences involved with increased outside air, a neutral zone also may be needed. In a triple-deck system, the outside air is brought by the heat exchanger to that neutral point, before entering the air stream. The result is returned efficiency to the HVAC system in its heating and cooling modes.
Another promising solution is the use of dessicants to pre-condition air without mechanical cooling.
For buildings undergoing major retrofits, the building’s air should be tested before renovations begin. Establish the levels of existing contaminants, if any, so that you have a point of reference. After renovations, the air quality should be retested. Periodically, additional IAQ tests should be conducted.
What should building owners do when indoor air actually is better than outside air, as often is the case in buildings located adjacent to major airports? Filtration for gaseous contaminants can play a major role in cleaning the building’s air. The health care industry already is aware of the importance of air filtration in controlling the spread of airborne pathogens. But other building owners are just beginning to recognize the importance of proper filtration systems.
Many advances have been made in HVAC control technology during the past decade. One of the most recent is the ability to control air flow, temperature and even air quality at individual workstations. Because of metabolism and dress in the office, women often complain that they are too cold, while men are too hot.
Advances in DDCs and control systems give us tools to get better air as well as energy conservation from HVAC systems. Everything now is automatic. We can set certain parameters for temperature and humidity with the outside air economizer.
And we can do so much more with the system to protect the health of the people inside the building. For example, if there is a fire and the smoke-detection system is activated, the HVAC controls can stop the air-handling system and start exhausting smoke from the space while alerting local fire and alarm departments.
Electronics in HVAC systems are becoming more integrated with each other: The air-handling unit knows how much is needed from it, and the chiller knows what each air handler is doing and can adjust itself accordingly.
Further refinements in HVAC system controls are on the near horizon. For example, comfort control that relies on more than the temperature to measure a space’s overall comfort currently is being investigated by researchers, consulting engineers, ASHRAE and building controls manufacturers. Sophisticated comfort control sensors are being developed that will take into account not just the dry-bulb temperature of today’s thermostats but also the mean radiant temperature, air velocity and humidity level.