Your questions answered: HVAC: Hospitals and health care facilities
On Thursday, July 25, 2019, presenters of the HVAC: Hospitals and health care facilities webcast tackled several questions. Those they were unable to address during the event are answered here. Providing cooling/heating comfort and energy efficiency in hospitals and health care buildings is an ongoing challenge for mechanical engineers. Emphasis on building performance, indoor air quality and adoption of energy-efficient building codes is increasing. Designs are based on a host of variables beyond space type and understood loads including operating costs, first cost, life cycle cost and measurement and verification requirements.
- Jeremy Jones, PE, EDAC, LEED AP, Healthcare Market Leader, Affiliated Engineers Inc., Chapel Hill, N.C.
- Cory Duggin, PE, LEED AP BD+C, BEMP, Energy Modeling Wizard and Principal|PEAK Institute, TLC Engineering Solutions, Brentwood, Tennessee
Question: Your HVAC comparison graph showed variable air volume with reheat as a “ low”first cost option. Don’t hospitals require return air terminal unit boxes and the corresponding increase in first cost?
Jeremy Jones: Return air boxes certainly make control easier, but I wouldn’t say they are “required.” The only areas I would consider nonnegotiable when it comes to return air control are spaces like operating rooms, especially if there is a night setback mode, where maintaining positive pressurization during varying load and flow conditions is necessary.
Question: Please provide additional information: It sounded like something about half of the refrigerant in variable refrigerant flow systems?
Cory Duggin: Section 7.2 of ASHRAE Standard 15-2016 sets the refrigerant concentration limit for high-probability system and references ASHRAE Standard 34-2016 Table 4- 1 and 4-2 where the limits are listed for each refrigerant type. Section 7.2.1 goes on to say that the refrigerant concentration limits listed in ASHRAE Standard 34 shall be reduced by 50% for all areas of institutional occupancies. This essentially reduces the allowable refrigerant charge of a VRF system by half.
Question: Can you speak to the requirements for maintaining laminar flow in an operating room?
Jeremy Jones: ASHRAE 170 provides many of the details. First, imagine a rectangle that extends 12 inches beyond the surgical table on the floor in both directions 70% of the ceiling area above this rectangle must be laminar flow air distribution. It should be low velocity (about 25 feet per minute, or less). This will likely not be enough by itself to satisfy the 20 AC minimum, so the remainder of the laminar flow diffusers should be as close as possible to the center. On the return side, all return within the room must be low. The bottom of the return grilles should be about 8 inches from the floor. The top can be no higher than the surgical table. Ideally, there will be four of these low returns, one in each corner, but sometimes you can only get two or three, because of all of the other items competing for space in the room. You must have at least two low returns that must be “remote from each other,” meaning opposite corners.
Cory Duggin:Yes, the energy efficiency section of the 2018 IgCC references ASHRAE 90.1 for many of its requirements and in some instances requires them to be exceeded. There is also an option by appendix to use the prescriptive energy compliance path from the International Energy Conservation Code rather than ASHRAE 90.1.
Question: Regarding active chilled beams: How do you ensure there is no shortcut airflow?
Jeremy Jones: As long as you stay within the manufacturer’s recommendations on primary air supply, they are specifically designed to avoid this.
Question: Can you confirm that the active chilled beams are essentially only acceptable in portions of the hospital that are not patient care?
Jeremy Jones: Not at all. In our experience they are perfectly acceptable in any space where ASHRAE 170 does not prohibit the use of recirculating room devices. That means that they are specifically allowed in most patient rooms, but not isolation rooms, operating rooms or intensive care units under current regulations.
Question: How much of the improvement is due to new equipment/construction, not the chilled beam?
Jeremy Jones: That’s a very fair question and one we don’t know how to isolate. Certainly the fact that the space was new construction helps in every aspect. The fact remains that the space, chilled beams and all, performs very well in every metric we measured.
Question: How do you supply only two air changes per hour instead of six air changes per hour with return air at four air changes per hour? There is also static pressure negative or positive required?
Jeremy Jones:Two air changes is all that is required from an outside air ventilation perspective. That’s what needs to be supplied to the room. The remaining air changes are always going to be recirculated, whether in the room or back through the air handling units.
Question: For dual-path air handling units, isn’t the unit actually smaller or same size (but taller) as standard single-path unit because the return air coil can be smaller because outside air load is treated separately?
Cory Duggin: Yes, the units are typically taller. The return air coil is smaller but the rest of the sections still have to be sized for the full airflow.
Question: What system is used in an operating room where an active chilled beam is in patient rooms?
Jeremy Jones: On this project, variable air volume with precision air terminals on both the supply and the return.
Question: For chilled beam systems, have you run into a scenario where the code minimum air conditioning was not enough to satisfy latent load of patient room?
Jeremy Jones: The only area where the code minimum is applied is the outside air ventilation quantity. The room load is met by providing the appropriate number and length of chilled beams.
Question: Did you specify chilled beams that incorporate condensate drainage as a precaution?
Jeremy Jones: No, we do not feel that this is necessary. As long as you sample room conditions to understand the dewpoint in the room and have a reset schedule on the secondary chilled water supply temperature to stay several degrees above dewpoint, this is not necessary.