PROPERLY DESIGNING AN ENGINEERED HVAC SYSTEM

Today’s SmartBlog post on designing an engineered HVAC system is written by Gary Miloradovich, P.E., the Principal of HVAC and Electrical Engineering Solutions, LLC. You can find out more about Gary’s company here.

There are two important factors that one should consider when designing an engineered HVAC system:

  1. A high level of indoor air quality (IAQ) and comfort
  2. Dependable, economical operation

To offer the highest level of Indoor Air Quality (IAQ) and comfort required, the system must provide the sufficient quantity of properly cooled and dehumidified air, as well as heating capability for colder seasons.  The supply air provided shall have an outside air component sufficient to remove indoor contaminants generated by respiration (carbon dioxide), cooking, new product off-gassing, odors, etc.  The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) offers excellent guidelines to assure IAQ and comfort in Standard 61.2 and their four volume Handbook.  See also the benefits of a BAS below.

In laboratory applications, sufficient outside air is necessary to replace air exhausted by fume hoods and local exhaust devices, and to provide sufficient room air dilution in the event of a spill within the lab.  Guidelines for minimum and recommended air changes per hour (ACH) vary from source-to-source; NFPA 45 requires a minimum of for ACH for unoccupied labs, OSHA recommends 6-12 AHU.  The maximum is considered 20 ACH to avoid excessive turbulence which will negatively affect the capture capability of exhaust devices.

For a dependable, economical engineered HVAC system, the designer should consider:

  • Consolidating cooling and exhaust equipment
    • The cost per ton of cooling and heating equipment decreases substantially as the capacity increases.
    • One large exhaust fan may replace numerous small fans, substantially decreasing total required horsepower and corresponding electrical cost.
    • Large units have superior longevity and dependability, reducing replacement and maintenance requirements.
    • Lower equipment count greatly reduces predictive/preventive maintenance and repairs.
  • Large units are typically more efficient; for example a large central chilled water plat may operate at a full load power consumption rate of as low as 0.5 KW per ton, while small distributed AC units may require over 1 KW per ton each.
  • Turn-down capability is much greater with a centralized system as opposed to operating numerous small units.
  • With a large central system the engineer and specify that the unit operates at its peak efficiency at the percent of full load that the geographical area experiences the highest number of hours annually.
  • Utilize a high quality Building Automation System (BAS)
    • A BAS allows precise control of all system components, assuring proper operation for superior IAQ and comfort.
    • Room pressurization control to prevent infiltration or ex-filtration of hazardous, odoriferous or any other unwanted fumes.
    • Remote viewing, monitoring, adjustment, and alarm capability are available.
    • A BAS system may be programmed to perform valuable predictive maintenance testing.
    • With the BAS in place, remarkable cost savings may be achieved. Calculations show that annual electrical cost may be reduced by as much as 39% by instituting the following:
      • Temperature, humidity and air flow setback during unoccupied times (nights, weekends, holidays)
      • Laboratory air flow reduction based on exhaust requirements. A typical laboratory often operates at less than 50% of peak design conditions.

We hope you have learned something in today’s post. If you have any questions about it, please feel free to contact us. We’d be happy to answer them.

Look for more from Gary “Milo” Miloradovich, P.E. in weeks to come. As always, thanks again for reading!