Many aspects of laboratory energy usage are not directly regulated by the baseline standards. However, these energy uses must be accounted for in order to obtain an accurate simulation of the building energy usage and properly calculate percent savings for green building ratings (tax deduction calculations only require consideration of regulated energy use, e.g. heating, cooling, fans, hot water and interior lighting). In addition, it is also important to note that the non-regulated energy components of the laboratory will impose loads on the regulated portions, such as chillers and boilers, increasing the importance of capturing this energy usage.
Laboratory HVAC Systems
Laboratories tend to be large buildings so the basic HVAC mapping rules presented in Chapter 6 will typically map to baseline building systems 5 through 8, which are variable air volume systems with one air handler per floor. There are three exceptions to this rule, however, that could affect the baseline building systems for laboratories:
- The first exception is specific for laboratories. This 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.)
- When the above exception for laboratories does not apply, a separate laboratory system may still be required to be modeled in the baseline building. Either system 3 (PSZ-AC) or system 4 (PSZ-HP) shall serve laboratories in the baseline building (depending on the heating source for the building) when one of the following conditions apply:
- Spaces on a floor have significantly different schedules or internal heat loads: heat gain differences of more than 10 Btu/h or operation schedule differences of more than 40 hours/week. (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." Many laboratory spaces with fume hoods would likely trigger this exception. (See the PRM, G3.1.1, Exception c.)
These special systems apply to the spaces that trigger one or more of the exceptions. The rest of the building/floor would be served by the baseline building HVAC system and air handlers.
The amount of internal load in a laboratory from equipment will vary greatly based upon function, and also will vary based upon time, with night-time loads typically much lower. The topic of diversity is addressed under the topic of schedules; however the peak load should be input based upon the actual equipment selection. In most cases, the equipment power will be the same for both the baseline and proposed design, except when the proposed design employs explicit strategies to reduce energy use and reduce internal loads, in which case, more efficient equipment or lower internal loads may be assumed in the proposed design. As an example, localized refrigeration equipment in the lab space might be replaced by a central chilled water system, thus reducing the heat rejection load that occurs in the space and increasing the efficiency of cooling the equipment. In this case, it would be acceptable to have different
internal loads in the baseline and proposed buildings. When equipment power or internal loads are different between the proposed design and the baseline building, special documentation shall be provided. Some common laboratory equipment is discussed in greater detail in subsequent sections.
In some cases it is standard practice to provide redundant equipment in laboratories because of the risk involved in equipment failure. If additional equipment is installed for pure redundancy, then this equipment shall be ignored in the modeling of the proposed design and the baseline building. For a more complex situation, a laboratory with a 100 ton load might be designed with two 75 ton chillers with the idea that should one chiller fail, the remaining chiller will be able to satisfy the critical load. If this design intent can be documented, then it is acceptable to model the proposed design in this fashion. The baseline building equipment will be autosized according to the rules in Chapter 2 and Chapter 6 and the number of chillers or boilers will be determined based on the rules in Chapter 6.
Space dry-bulb temperature setpoints should generally be based upon actual design requirements, but for laboratories will generally be around 70°F for heating, 72°F for cooling. Humidification to at least 30% RH is common in most areas of the country. Dehumidification, when required, is accomplished by keeping coil leaving air temperatures around 53 F during humid ambient conditions.
For systems serving laboratory spaces, use a supply-air-to-room-air temperature difference of 17°F for the baseline building and the proposed design (Chapter 6 specifies 20°F for other building types). If return or relief fans are specified in the proposed design, the baseline building design shall also be modeled with fans serving the same functions (this is the general Chapter 6 modeling rule). The baseline building return/relief fans shall be sized for the baseline system supply fan air quantity less the minimum outdoor air, or 90% of the supply fan air quantity, whichever is larger. See the discussion above on laboratory HVAC systems for more detail on exhaust systems serving fume hoods.
Due to the presence of hazardous materials in laboratory environments, it is common practice to use 100% outside air. The codes do not explicitly forbid lab air recirculation within individual lab zones, but code requirements are most easily met by a 100% outside air system. The Chapter 6 modeling rules apply in this case, as the outside air for the baseline building is the same as the outside air for the proposed design.
In some cases, labs are part of a mixed-use building that includes both office spaces as well as laboratories served by the same air handling system. In most cases, the baseline building system serving laboratories will be separate from the main building system (see laboratory HVAC systems above).
Outside air delivered by these dedicated systems would be the same as the air delivered by the proposed design systems, unless the assignment of thermal blocks to systems is modified.
Appendix C has schedules for laboratories that shall be used as a default. The schedules assume heavier loads during more typical working hours. Fans are assumed to be on 24 hours throughout the day. If the laboratory operates on a seasonal schedule, such as a school schedule, and has lower usage during one season, adjust the schedules as needed.
Open animal cages that do not include their own dedicated ventilation system are commonly used in laboratories. These shall be the same in the proposed design and the baseline building.
These systems use high pressure steam for sterilization. Typically efficiency measures accounted for here would be on the steam side.
Compressed Dry Air
Some laboratories require a supply of compressed dry air for drying and other purposes. When these systems exist in the proposed design, they shall also exist in the baseline building. In the baseline building, the supply air pressure setpoint is constant and the systems do not employ heat recovery. The air dryers are regenerated with compressed air, on a regular time-based interval. Energy efficiency measures may be documented for the proposed design with proper documentation.
These systems remove minerals and ions from the water to reduce the electrical conductivity of the water and would typically be the same in the baseline and proposed buildings.
Heat pumps typically heat or cool the interior of the chamber to provide a controlled test environment. For the baseline building, heat rejection (or absorption) from the heat pumps is assumed to occur directly into the space in which the heat pump is installed. The proposed design may employ energy efficiency measures, including high efficiency heat pump units, as well as remote heat rejection through a condenser water system.
Fume hoods generally do not contain local fans, but rather have an exhaust system serving multiple hoods. The energy use of a fume hood is reflected in the amount of air moving through the hood and the efficiency of the exhaust system that serves it. Fume hood exhaust systems in the proposed design can be operated as constant air volume (CAV) or variable air volume (VAV). The baseline building exhaust system shall be VAV for laboratory exhaust systems that are designed for 5,000 cfm or more. See laboratory HVAC systems above. Otherwise, the baseline building exhaust fan system and operation shall the same as the proposed design. The modeling assumption for the sash opening face velocity is a constant 100 ft/min for both the proposed design and the baseline building, regardless of space occupancy and regardless of whether an occupant is standing in front of the hood. However the baseline hood exhaust schedule assumes the hoods are closed and airflow reduced during unoccupied periods.
Biosafety cabinets can also be operated as CAV or VAV. However, biosafety cabinets have a more demanding tolerance (+/-5%) on variations in air flow than fume hoods. The air flow variation in a typical VAV system is on the order of +/-1for biosafety cabinets is CAV.
These machines will wash and sterilize lab glassware. The equipment will typically be the same in the baseline and proposed buildings. This equipment has high but intermittent heat and moisture gains to the containing spaces.
Process vacuum pumps create a negative-pressure distribution system needed for certain types of lab equipment. Not to be confused with the “house” vacuum system, used for janitorial purposes. In most cases, the baseline and proposed vacuum pumps will be the same, although more efficient vacuum pumps could be substituted in the proposed design with suitable documentation of what is considered a typical base case condition.
Reverse Osmosis Water
These systems are similar to the de-ionized water systems except that the process involves pumping the water through a semi-permeable membrane. These systems would typically be the same in the baseline and proposed buildings. Average loads should be far below design electrical capacities.