Many health care projects are designated as occupancy group "I", which subjects them to specialized code requirements necessary based upon health and safety requirements. Typically, the envelope components of health care projects are not that different from conventional occupancies. However, lighting, HVAC and domestic hot water systems can be significantly different and will present some challenges in the modeling process. In addition, these facilities can have many other energy consuming systems that will require attention.
Health care projects typically have a wide range of space uses. A typical hospital could have 50 or 60 different space functions occurring in the facility. In modeling the facility, there are two possible choices for lighting. The easiest choice is to use the building classification method for all spaces that occur in the building. The second choice is to break the building out into each space function and use the space-by-space method, which will entail a significantly larger amount of work. Choosing the approach can be difficult, as a facility with a large amount of space functions requiring large amounts of light would benefit from the more granular approach of using the space functions. Given the fact that a hospital might require HVAC zoning of several hundred zones, the additional work of layering in space function lighting can result in models with zones numbering 600 to 1000. In either case, the baseline and proposed buildings will have the same thermal blocks, zoning and space functions.
An additional consideration is that many spaces in the proposed design may use task/ambient lighting systems. For example, patient rooms will typically have an ambient lighting system that provides minimal illumination, and a second lighting system that will only be activated by staff during brief examination periods. Other areas, such as surgery rooms, will have surgical lights that are only used during active surgery, so it is important that the lighting systems include appropriate schedules for the task lighting that accounts for the intermittent use. Note that in modeling the baseline building, the baseline lighting power density allowance will be modeled, using the ambient lighting schedule from the proposed design. An alternative schedule may be used for task lighting in the proposed design. For exempt lighting uses, this alternative schedule shall be used for both the baseline building and the proposed design.
The basic HVAC system mapping rules described in Chapter 6 apply to health care facilities. Most are large buildings so the baseline building systems will tend to be system 7 (VAV with hydronic reheat) or system 8 (VAV with parallel fan-powered boxes and electric reheat). However, many spaces in healthcare facilities trigger the exceptions to the HVAC mapping rules:
- The laboratory exception applies when a laboratory or group of laboratories have an exhaust system designed for 5,000 cfm or more of air movement. The baseline building system serving the laboratory spaces shall be either system 5 (PVAV with hot water reheat) or system 6 (PVAV with parallel fan- powered boxes and electric reheat), depending on the heating source in the building. The PVAV system must be capable of reducing the exhaust and makeup air volume to 50% of design values during unoccupied periods. This exception essentially requires VAV for both the supply fan and the exhaust system. (See the PRM, G3.1.1, Exception c.)baseline?
- When the above exception for laboratories does not apply, a separate system may still be required to be modeled in the baseline building. Either system 3 (PSZ-AC) or system 4 (PSZ-HP) shall serve healthcare spaces in the baseline building (depending on the heating source for the building) when one of the following conditions apply:
- Spaces have significantly different schedules or internal heat loads. Heat gain differences or more than 10 Btu/h or operation schedule differences of more than 40 hours/week trigger this exception. (See the PRM, G3.1.1, Exception b.)
- Spaces on a floor have "special pressurization relationships, cross-contamination requirements, or code-required minimum circulation rates". Surgical suites and other healthcare spaces would likely trigger this exception. (See the PRM, G3.1.1, Exception c.)
The HVAC systems in many healthcare facilities are in operation 24 hours per day and consume very large amounts of energy. In many cases, the decision of a certain type of mechanical system in these facilities is made for health and safety code compliance, and in many cases they will be 100% outside air systems. It is not unusual to see very large static pressure requirements due to HEPA filtration and sound attenuators. In the case of 100% outside air systems, exhaust fans are also an important aspect of the design. Given the large diversity of space uses, and the fact that each may have specialized ventilation requirements, it is important to model the building with a sufficient number of zones to account for these uses. In modeling the baseline building, the same zones are used with the same ventilation rates used in the proposed building. These conditions will likely trigger one of the exceptions to the HVAC mapping rules and require that the spaces be served by a separate system.
Some healthcare facilities will have areas that are used continuously, such as patient rooms, mixed in with areas that are only in use during normal daytime hours, such as medical offices. In some cases an entire wing or floor of a facility will be on a normal 8-5 operation and will have a dedicated HVAC system to allow night-time shutdown. In this case, the proposed building modeling should include appropriate HVAC operating schedules to account for the night-time operation. The baseline building will typically have separate systems for spaces with a different schedule (see discussion above).
Most areas of hospitals have relatively high airflow minimums and require continuous operation even when unoccupied. Some areas do not allow VAV operation or require return air VAV valves to assure pressurization. Some areas of the building will have very large air change rates, such as surgical suites. However, in many applications, these suites are only used during daytime hours. One strategy is to have a night setback in these spaces, reducing the air change rate from 20 in the daytime, for example, down to 6 at night. This will require the proposed building to include schedules to account for this, but in the case of the baseline building, operation would be assumed to be at the 20 air change rate for all hours.
Surgical suites may also require low SATs and special dehumidification. Most hospitals require winter humidification, varying among systems and zones.
Domestic Hot Water
Domestic hot water usage will vary greatly depending upon the type of facility, as well as functions that occur in the facility. Some hospitals have on-site laundry facilities, while many others out-source this activity to offsite providers. Facilities such as medical office buildings will have dramatically lower hot water usage than a multi-bed facility with many patient rooms. Once again, accurate schedules that reflect this usage will need to be developed. In most cases, the baseline and proposed buildings will include the same hot water usage and schedules, unless a reduction in hot water usage can be demonstrated due to a proposed design feature that is not required by or typical of the baseline building. An example might be a laundry facility that uses water saving equipment. Other energy savings in the proposed building could come from the boiler efficiency and possibly the recirculation pumping system.
A wide range of internal loads exist in healthcare facilities, ranging from television sets in patient rooms to radiology equipment in labs, all running during different hours of the day. Most internal loads are reduced to a minimum at night while a facility is fully staffed in the daytime. There will be a need to develop equipment operation schedules to reflect this operation. In addition, given the fact that some equipment will only run a few minutes out of the hour, such as an MRI machine, it is important not to overestimate the loads attributed to the equipment. In most cases, the baseline and proposed building models will include the same equipment loads and operating schedules, unless the modeler can clearly demonstrate a more efficient piece of equipment is being used compared to standard practice or code minimum.