There are no industry standards for rebalancing HVAC water systems, so it got me thinking about the topic and I came up with several questions pertaining to rebalancing chilled water, condenser water, and hot water heating systems. With each question, I filled in my thoughts based on my own knowledge of various HVAC applications using health care facilities for my discussion.
Inpatient Hospitals: These buildings are intended to be built with an eye to maximum equipment life cycle because hospitals are intended to be around for several years. Within each hospital is a wide range of HVAC applications to satisfy patient room comfort, minor and major treatment rooms for safe operation, and infection control care of patients, to mention just a few rooms. There may be medical research occurring and the hospital may be a teaching hospital, which further expands the HVAC applications within the health care facility. The hours of operation will include 24-7 occupancy for much of the facility, but will also have occupancy hours of 7 a.m. to 5 p.m., Monday through Friday for administration spaces.
Rebalancing Hot Water Heating (HWH) Systems For Health care
HWH systems serving the perimeter of the building will operate 24 hrs/day for approximately four months of the year for those states north of latitude 35 degrees to latitude 40 degrees. Depending on the specific HWH system and the number of terminal units heating the building perimeter, these systems may want to be rebalanced every 10 years. For buildings north of latitude 40 degrees, where the heating system will probably operate 24 hrs a day for approximately six months of the year, you may want to rebalance more often. If you simply figure these HWH systems will operate 50% more hours than HWH systems below latitude 40 degrees, then maybe the facility operator will want to rebalance these systems every five years.
Why rebalance? The buildings are operating 24 hrs/day for those months listed above. Do you ignore the fact that these systems were installed to provide space comfort with some systems operating year-round to assist in humidity control? Analogous to owning a home, do you ignore your heating system as time goes by? Also, rebalancing will improve energy consumption costs.
Rebalancing Chilled Water Cooling (CHWC) Systems For Health care
CHWC systems for the most part serve the entire building and will operate 24 hrs/day for approximately four months of the year for those states north of latitude 40 degree. Depending on the specific CHWC system, the cooling coils will provide mechanical cooling to air condition the building interior as well as exterior, and they may need to be rebalanced every 10 years. For buildings south of latitude 40 degree where the air conditioning system will probably operate 24 hrs/day for approximately six months of the year, the exterior facility operator may want to rebalance these systems every five years.
Why rebalance? Air conditioning systems provide space comfort, humidity control, and dehumidification control where all three of these HVAC requirements are mandated in health care facilities. Hospitals are designed to operate this way on day one of occupancy. So do you ignore the basis of design over time? If that is the case, maybe building operators should ignore cleaning the windows, cutting the grass, or shoveling the snowy walkway over time. Then again, do you really need to change filters or calibrate space thermostats? How does water rebalancing get left off the to-do lists as facility support deliverables?
I have used health care as an example of rebalancing needs, and I have yet to find any industry standard that requires or recommends rebalancing, but I put this thought out here in this column to get readers thinking about the hospital they go to on occasion.The same applies to all those other HVAC applications you can read about in the ASHRAE 2011 Application Handbook (e.g., schools, office buildings, etc.) where each application has its own basis-of-design requirements that will be linked to air and water balancing. So why does rebalancing not have industry standard requirements that can assist in efficiently maintaining the building over its lifetime?