Medical Construction & Design

JAN-FEB 2018

Medical Construction & Design (MCD) is the industry's leading source for news and information and reaches all disciplines involved in the healthcare construction and design process.

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MCDM AG.COM | JA N UA RY/ F EBRUA RY 2018 | Medical Construction & Design 49 that aff ects a physician's offi ce, that may be tied to the same condensing system as the radiology suite across the hall. The repair for this issue would require the entire sys- tem to be drained, the leak fi xed and the entire system to be recharged after a com- missioning eff ort is completed. This repair may take hours or even days, depending on the complexity of the leak, access to the equipment, etc. STEP #3 Consider maintenance The next concern, which ties into the above-mentioned scenario, is how the facility will be staff ed for maintenance personnel. VRF is seen as a simple solution that does not require highly trained staff to maintain, and therefore full-time staff need not be allocated at each building site. This however, is not always true. Due to the distributed design of the fan coils in a VRF system, regular maintenance is required in more locations around the facility. Filters need to be changed monthly, fans need to be balanced and controls need be calibrated. If staff is not located at the project site, the design engineer needs to consider more self-diagnostic tools, controls that alarm remotely when there is an issue, keep detailed preventive maintenance schedules and receive alarms from various HVAC systems within the facility outside of the VRF equipment. Just as everything else in the design engineering world, VRF is a tool that needs to be used correctly. It is not a solution that can be implemented blindly. Healthcare facilities have specifi c and purposeful requirements for HVAC system design. These requirements are focused on patient health and safety, which also needs to be the focus of any successful HVAC healthcare design project. Local and state codes, industry guidelines and engineering best practices enforce these requirements. VRF systems can meet these requirements, but designers need to be careful about a couple of specifi c details. STEP #4 Consider fi ltration The fi rst is fi ltration. In a typical com- mercial building, the HVAC system can be fi ltered with a MERV-8 (30 percent) level of fi ltration, which removes partials down to approximately 3-10 microns, which creates a relatively low level of pressure drop. VRF systems are designed to work well with the low level of pressure drop. It helps the VRF system function with low fan energy, low noise and lower fan stress. Unfortunately, in many functions within a healthcare facility, higher levels of fi ltration are required to provide the necessary level of patient health and safety with a typically minimum fi nal fi lter with a MERV-13 (90 percent) level of fi ltration, which removes partials down to approxi- mately 1-3 microns, the commonly accept- able size ranges for sneezes. This stops airborne particles from patients propagat- ing to other areas of the facility, which increases the potential for healthcare asso- ciated infections. The higher level of fi ltration during op- eration creates a higher level of pressure drop and often strains most VRF system fan coil options past the point at which they can maintain catalog performance values for total airfl ow, and sometimes heating/cooling capacities in severe instances. During design, engineers need to consider external pressure drop limita- tions with the increased fi ltration require- ments. They should create smaller zones with less ductwork distribution down- stream from the fi nal fi lter to the register outlet or alternate fan coil types to achieve the desired airfl ow and cooling. STEP #5 Consider air change rate The second detail to consider is the air change rate. Unlike commercial projects that typically have airfl ow determined by space heating/cooling requirements, healthcare facilities are often required to meet a minimum amount of air changes. This means they need to replace the vol- ume of air a prescribed amount of times based on the room's volume. The total airfl ow is typically higher than calculated for heating/cooling requirements and therefore creates a circumstance where the nominal airfl ow required for a ton- nage of equipment is not in line with the cooling needed on a hot summer day, for example. With a traditional chilled water cooling system, this would not be an issue because it can be designed to be highly variable. With a VRF system, the equipment is available in stepped sizes, which does not allow for a precise fi t of capacity to load. During design, engineers need to con- sider the calculated heating and cooling requirements for the healthcare spaces and consider a higher level of available diversity when selecting the condensing sections of the VRF system. This will allow for right-sizing more equipment, reducing energy consumption and initial installa- tion costs for the project. Any HVAC solution has its tradeoff s and each solution fi ts a specifi c healthcare facility owner best. The design engineer's responsibility is to ask the right questions early and often and to provide valuable feedback to educate the owner about what they are signing up for. The engineer needs to consider not only design considerations but also what the owner will be left to work with when the project is complete. For example, is trained facility staff available at the project site? Will the VRF system be properly commissioned? What are the operating schedules for each department within the facility? What kind of fi nancial impacts will the facility suff er if the VRF equip- ment malfunctions? Is the control system confi gured to provide the pertinent information to the right staff ? These are all questions that will aff ect the decision- making process. VRF is here to stay and will most certainly grow further over the coming years as equipment prices con- tinue to drop. Mikhail Fuks, P.E., is studio manager and mechanical engineer at P2S Engineering, Inc. 1982 Year the world's fi rst variable refrigerant fl ow control was introduced — 20.9M Square footage of outpatient MOB space completed in 2017 —

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