Healthy hospital success: HVAC


Another relevant example would be the VA-San Diego surgery suite retrofit and expansion. We were awarded the task of providing a design based on a study we initially prepared that included a three-way side-by-side economic analysis meant to guide decision making. We had to convert a return-air HVAC system sized to serve the existing hospital surgery suite (unsatisfactorily) into a 100% outdoor-air HVAC system to serve a larger-capacity surgery suite that, unlike in the past, was supposed to offer the capability to maintain significantly colder and drier indoor space conditions. An existing deficient humidification system had to be tackled as well as part of the task. The existing humidification system consisted of one large centralized steam humidifier installed upstream of all OR serving branches. The previous designer's choice of humidification system was driven by that lack of space (not sufficient sorption duct length available at each OR branch to handle the OR humidification load). The downside of such an approach was the fact that all ORs had to accept the humidity level consistent with the highest humidity level required by any of the ORs at any given time (though each OR had the ability to provide independent temperature control). To provide each OR with independent temperature and humidity control, our approach was consistent with providing an intermediary humidifier (supplying air consistent with to the lowest OR dewpoint to be maintained) while we provided on each OR's branch a final small-sized humidifier (consistent with very short sorption duct length requirements).

CSE: What indoor air quality (IAQ) or indoor environmental quality (IEQ) challenges have you recently overcome? Describe the project, and how you solved the problem.

Schultz: Protective environment rooms for oncology patients require a high air-change rate as well as nonaspirating laminar flow panels near patient beds. A primary concern is patients' comfort, as they are sensitive to fluctuations of air temperature and movement. To minimize the discomfort, the laminar flow panels should be located adjacent to the bed's footprint and the supply air rate-of-change can be strictly controlled to minimize fluctuations in room temperature. Additional perimeter radiant heat can be applied to address skin loss at windows or help minimize condensation on window frames.

Rome: Pharmacies are tested annually to the U.S. Pharmacopeial Convention standards and guidelines. The particle concentrations demand a combination of systems and strategies using high air changes, HEPA filtration, and air-device delivery. We recently have effectively reduced air changes by using strategies employed by our containment laboratory group to improve air distribution in the space. This saved energy, overall system effect, and first cost.

Heim: Recently, we were challenged to design orthopedic operating rooms to maintain a space condition of 58 F at no more than 55% relative humidity. All of this had to be done using standard chilled water of 44 F. Our solution was to provide a dedicated AHU that would produce standard discharge conditions of 55 F. That air was used to serve the support spaces, and the remainder was sent through a desiccant wheel dehumidification unit, which drew additional moisture out of the airstream and conditioned the air back down to 50 F for delivery to the space.

CSE: Have you specified more alternative HVAC systems on hospital projects recently? This may include displacement ventilation, underfloor air distribution, variable refrigerant flow (VRF) systems, chilled beams, etc.

Heim: RMF has more frequently recommended alternative HVAC systems. RMF has used VRF systems in specific situations, but hospitals typically have campus chilled-water and heating-water/steam systems in place, which makes it a hard sell to use alternative utilities. I have begun to see more of an acceptance of chilled beams as well.

Shah: PBS Engineers consistently offers its clients (when required) side-by-side economic analyses. We believe that there is almost always more than one possible solution for each HVAC design task a particular building may require. Therefore, we provide (where required and/or applicable) options and alternatives at the level of single-line/schematic diagram and guide our clients through the decision-making process, clearly and transparently present pros and cons associated with each option/alternative. At Animal Research Center Facility-VA North Hills (Simi Valley), we designed the HVAC system (including the air distribution consisting out of central diffuser screen supplying laminar airflow to the operating table surrounded by air curtain supply linear slot diffusers where applicable). In a typical operating room, where the OSHPD is not required, we tend to apply the American Institute of Architects (AIA) Guidelines that specifies a minimum exchange rate of 15 air changes/hr (ACH). These guidelines only address minimum standards for the air distribution and thermal-control systems. Most hospitals have standards (like OSHPD) that require higher air-exchange rates than the minimum AIA standards. There are other guidelines (again, where the OSHPD is not the governing entity) such as ASHRAE and the Centers for Disease Control and Prevention.

Rome: Outpatient health care facilities/areas have recently been employing alternate strategies such as VRF, chilled beams coupled with energy-recover outside air delivery, and displacement ventilation. A recent inpatient facility we designed is using a 100% outdoor air (OA) system with dual-wheel energy recovery for patient rooms where the VAV terminals at each room have decoupled heating and cooling. It is a similar concept to the systems used in the outpatient facilities, but it keeps the wet systems in the corridor outside the patient room for maintenance and access.

CSE: Describe a challenging building envelope project you recently designed in a hospital.

Schultz: Condensation-resistance qualities of building envelopes need to be more robust in hospitals than in other building types, primarily because these humidified buildings generally operate between 25% and 35% rh. The temperature and relative humidity setpoint criteria should be established early on so the building envelope can be specified to accommodate the indoor air conditions minimizing surface condensation. Once the building envelope begins fabrication, the condensation-resistance performance is fixed and opportunities for adjustments may no longer be available. Wall and glazing manufacturers can run simulations on specific window assemblies to demonstrate that their systems will not result in a surface temperature below the indoor wet bulb during the winter. Establishing the indoor minimum relative humidity along with the dry-bulb temperature during the schematic design is needed so the architect and builder understand the criteria they need to accommodate with the building envelope.

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