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July 23, 2015
In an era when hospital heating, ventilating and air conditioning systems are getting more complex and expensive in the interest of energy efficiency, Whidbey General Hospital in Coupeville chose to pursue a simpler approach to energy efficiency for its 60,000-square-foot patient care addition. The end result may very well prove to be a guiding light for many hospital projects in the future.
Traditionally, hospitals rely on a temperature control concept known as “reheat” where large, centrally located ventilation equipment delivers cold air (24 hours per day, 365 days per year) to hundreds of rooms simultaneously. The air must be delivered cold, as some interior rooms will always need cooling. Rooms that don’t need cooling have individual heating coils that heat the cooled air back up to room temperature, hence the term reheat.
Reheat became popular decades ago when energy was cheap and labor was expensive. A primary benefit of this traditional concept is that much of the required maintenance, such as filter changing, greasing of bearings and adjusting fan belts, can be done centrally and efficiently. Maintenance staff were often stationed near central equipment rooms so they could keep an eye on things.
The concept is not energy-efficient. Energy is required to cool massive amounts of air at the central equipment and then additional energy is required to heat much of that air back up at individual rooms.
As much as 40 percent of all energy consumed by a hospital is used for reheating. Newer hospitals with ample budgets have invested additional funds on complex airflow-reduction strategies and more efficient condensing gas boilers and/or industrial heat pump systems to produce the heat.
Another disadvantage of the traditional concept is the thousands of feet of ductwork needed to transport air between distant rooms and central equipment, typically requiring hundreds of kilowatts to power fan motors. The large ductwork requires space, adding more floor-to-floor building height and construction cost. Lint and dust accumulates (sometimes as much as a half-inch thick) inside the “return” ductwork that transports unfiltered air and contaminants from individual rooms back to central equipment.
An alternative system
Whidbey General cannot afford to waste energy nor can it afford the expensive add-ons to improve the efficiency of a traditional system. It was time to get creative!
HDR Architecture’s engineering consultant, Coffman Engineers, suggested an efficient alternative to the traditional system. While this alternative system will meet hospital codes and use much less energy, the hospital was advised that this may be the first significant hospital project to employ the concept in the United States.
The hospital was still interested, especially its sustainability coordinator. The hospital’s contractor, Andersen Construction, then confirmed that the alternative fits the budget, and the green light was given.
This alternative concept is commonly referred to as a “variable refrigerant flow” (VRF) heat-pump system, and has rapidly become popular for smaller commercial (non-hospital) buildings throughout the United States. The VRF concept was developed in Japan decades ago and caught on in Europe long before the United States.
Coffman started specifying VRF for hotels 10 years ago when it was still virtually unknown here. The concept employs localized heat pump condensing units mounted outdoors or in closets linked with small refrigerant pipes to fan coil units in or near rooms being served.
Each condensing unit can serve multiple fan coil units. Each fan coil unit offers occupants independent temperature control and requires minimal ductwork since it is located in or near the room(s) served.
A condensing unit only provides heating or cooling to a fan coil unit if needed, no continuous central cooling or reheating. As an added benefit, the condensing unit will use the heat removed from one fan coil unit that is cooling and transfer it to another fan coil unit that is heating, essentially providing free heating with no added energy.
The VRF concept is economically scalable. Large hospitals could have a hundred closet-mounted condensing units networked together with a water loop, allowing heat to be shared across an entire campus.
This same water loop could also be used to cool computer servers and medical equipment, allowing traditionally wasted energy to be used to heat patient rooms. Hospitals fully utilizing VRF may burn little or no fossil fuel.
Breaking an industry of old habits means confronting objections upfront. Every concept has disadvantages that traditionalists are quick to point out. The trick is to turn some or all of those disadvantages into advantages. For example:
• Difficult service access. Individual VRF systems must be kept small to comply with refrigerant codes. A small hospital may need a couple of dozen localized VRF systems, which means more equipment to maintain, distributed across the facility, and often in areas with difficult access.
A valid concern, but one needs to consider the overall reliability of modern, highly engineered products assembled and tested in a climate-controlled manufacturing facility. One must also consider how maintenance-free products have become in recent years.
The advantages of distributed small systems are many: A failure of a system would impact only a small portion of the hospital. Small equipment is typically deemed “rugged” by building officials and not in need of expensive seismic certification required for larger equipment in hospitals.
Seismic bracing is not needed for the small ductwork and durable refrigerant piping in a VRF system. VRF systems employ reliable, self-diagnosing controls that communicate directly with central work stations.
• Filter replacement. Each fan coil unit has a filter that requires frequent replacement. Filters are typically located above ceilings, adding maintenance cost.
But is this really necessary? For Whidbey General, Coffman minimized this disadvantage by locating return air filters above convenient, hinged grilles at the entrance to each patient room. It is possible to replace the filter in less than 60 seconds using a small step stool.
Coffman further refined the design by oversizing the filter, a trick that reaps huge rewards. By doubling the size of filters they will actually last four times longer, virtually eliminating the maintenance “disadvantage” and reducing overall filter cost.
• Air quality. Hospital codes require more stringent filters for large central systems (MERV 14) than for patient room fan coil units (MERV 6). MERV stands for minimum efficiency reporting value. The higher the number, the higher the filtration effectiveness.
Why not raise the bar? Coffman specifies new filter technology that has made inexpensive MERV 11 filters available for small applications like fan coil units. MERV 11 filters are very effective, so dust accumulation is not a problem inside return ducts and the fan coil unit.
Patients at Whidbey General will breathe air that was recirculated only from their own rooms through short, clean ducts filtered to MERV 11 standards. Compare this to patients at other hospitals who must breathe air that is recirculated from other patient rooms through hundreds of feet of potentially dirty ductwork before it is filtered centrally to MERV 14 standards.
MERV 14 filters are better than MERV 11, but they are not perfect so one needs to ponder which concept is more desirable considering the potential source of contaminants that could get past the filter.
The Whidbey General addition is now starting construction. The University of Washington’s Integrated Design Lab and Solarc have now joined the project team and are doing computer modeling to determine just how much energy will be saved.
The team has targeted the maximum rebate from Puget Sound Energy, which requires a 25 percent reduction in energy usage from code requirements. The Integrated Design Lab has developed energy reduction strategies specifically for hospitals in their research to target an energy use index, or EUI, of 100 or less, compared with conventional hospital construction, which runs in excess of an EUI of 200 or more.
The mechanical and electrical systems will be bid in August. Stay tuned!
Don Iverson is a LEED-accredited mechanical engineer and principal at Coffman, with more than 37 years of award-winning design experience in the health care industry.