The Convergence of Standard 90.1, 62.1 and 55: Examples of Energy Efficiency Measures.
Energy, indoor air quality, and thermal comfort are three most important pillars in ASHRAE that have fundamental impacts in HVAC&R industry. Prior to 1970, building design and operation in the U.S. was conducted on a "business as usual" basis. However, the oil embargo of 1973 precipitated the first global energy crisis (Hunn 2010). In the aftermath, ASHRAE Standard 90-75 and Standard 62-73 were developed in the early to mid 1970s. Decades after, the standards have been continuously maintained; Standard 90.1 and 62.1 have been adopted to International Energy Conservation Code (IECC) and International Mechanical Code (IMC) respectively. All three standards (90.1, 62.1, and 55) have been established to provide acceptable indoor air quality and thermal environmental conditions for human occupancy while optimizing energy efficiency in built environment.
Standard 90.1 is the energy standard for most regulated buildings except low-rise residential buildings. It covers building systems which contribute to energy consumption, including Building Envelope (Chapter 5), HVAC (Chapter 6), Service Water Heating (Chapter 7), Power (Chapter 8), Lighting (Chapter 9), and Other Equipment (Chapter 10).
In general, 90.1 provides three compliance paths documented in Administration and Enforcement (Chapter 4), which are prescriptive, energy cost budget, and performance rating method. This is unique in ASHRAE standards, and it offers great flexibility for architects and engineers in integrated design process.
The standard not only should be followed by architects and engineers (e.g. design engineers, energy engineers, and commissioning authorities), but it also has significant impact on regulated building equipment manufacturers. For example, the minimum equipment efficiency tables in Chapter 6 defines the bottom line efficiencies for most regulated HVAC equipment.
90.1 has been adopted to IECC in the current code cycle (every 3 years) and has been one of the compliance paths for commercial buildings in IECC. It means architects and engineers can choose either 90.1 or IECC to follow, which is also subject to local code jurisdiction.
Standard 62.1--Indoor Air Quality
Standard 62.1 is the standard for acceptable indoor air quality by regulating ventilation design and operation. Comparing with most building systems covered in 90.1, Standard 62.1 primarily focuses on HVAC ventilation systems.
The compliance path to 62.1 is prescriptive. The standard is mainly used by consulting engineers and researchers, and one of the most widely used sections in 62.1 is the minimum ventilation rates tables, which establishes the ventilation design baseline for most of occupancy categories. 62.1 has also been adopted to IMC in the current code cycle.
Standard 55--Thermal Environmental Conditions
Standard 55 is basically the standard for thermal comfort for human occupancy. Comparing with different building systems covered 90.1 and 62.1, Standard 55 primarily focuses on people instead of systems or equipment.
The compliance path to Standard 55 is prescriptive. The standard is mainly used by consulting engineers and researchers, and one of the most widely used sections in 55 is the graphic comfort zone method on psychrometric charts, which provides the design and operation ranges in occupied spaces. Standard 55 has not been adopted to International Building Code, but it is the ASHRAE standard addressing the most common HVAC issue--thermal comfort.
Table 1 summarizes the comparison for Standard 90.1, 62.1 and 55. These three ASHRAE standards together contributes to the three most important subjects in ASHRAE: energy, indoor air quality, and thermal comfort.
EXAMPLES OF ENERGY EFFICIENCY MEASURES
In existing buildings, energy efficiency measures (EEMs) are identified and implemented for energy efficient operation, maintenance, management, and monitoring. The concepts of the EEMs can also be applied to new construction and major renovation.
The following examples of EEMs are presented to explain the convergence of Standard 90.1, 62.1 and 55--to provide acceptable indoor air quality and thermal environmental conditions for human occupancy while optimizing energy efficiency in built environment.
Building Envelope--Attic Roof Insulation
An example of building envelope EEM is presented below--replacing attic roof insulation.
ASHRAE Standard. Chapter 5 of Standard 90.1 is building envelope, in which "all roofs shall comply with the insulation values specified in Table 5.5-0 through 5.5-8" per section 126.96.36.199 roof insulation under section 5.5 prescriptive building envelope option. Minimum insulation of R-49 (or maximum assembly of U-0.021) is required for attic roof in residential buildings (except low-rise residential buildings) in climate zone 5A per Table 5.5-5. It is noted that Standard 90.1 is used for evaluating this EEM recommendation rather than indicating code application for any specific project.
Standard 62.1 and Standard 55 do not address ventilation and thermal environmental conditions in vented attic space. However, the attic space above the insulated attic floor requires adequate venting to (1) eliminate moisture that transpires through the ceiling from conditioned space below and (2) to prevent melting snow and ice from forming ice dams at the eaves. Passive roof vents are usually located in soffits, dormers, and at roof peaks.
Existing Condition. Five residence halls on a university campus located in climate zone 5A were originally constructed from 1930s to 1960s. All building attic roof structure includes a flat upper section with ethylene propylene diene monomer (EPDM) roofing material and sloped sides with original slate shingles. The roof structure consists of a solid wood deck supported by wood and steel structural framing below.
The attic space is vented through roof dormers, with a layer of cellulose insulation between the attic floor joists. The cellulose insulation thickness is approximately 3.5 inches and it is not uniformly distributed. The R-value of the existing layer of attic insulation is estimated R-11 based on the thermal conductivity (k-value) of loose fill cellulose fiber insulation from Chapter 26 Heat, Air and Moisture Control in Building Assemblies--Material Properties (ASHRAE 2017).
Additionally, many cracks and unrepaired penetrations through the ceiling into the attic space and the lack of effective air and vapor barriers resulted in excessive air leakage from the conditioned space below into the vented attic. In the attic, plastic sheets are used to temporarily direct water from roof leaks away from the cellulose insulation. In the conditioned space below, evidence of roof water leaks was identified in several locations throughout the buildings.
Recommendation. Sealing ceiling openings and adding insulation to the attic floor can reduce (1) heat conduction through the ceiling and (2) heat loss from uncontrolled air leakage and exfiltration into the attic space.
To seal the attic floor, the existing cellulose insulation would first be removed and the attic space vacuumed, and the cracks and penetrations through the ceiling of the top floor would be repaired and sealed. To create an effective air seal of the attic floor, a 2-inch thick layer of closed cell spray foam insulation would be applied to the entire attic ceiling with careful attention given to seal between attic floor joists and around structural beams. Applying a 10-inch thick layer of blown-in cellulose insulation above the spray foam layer would further reduce heat conduction loss and air leakage throughout the entire attic floor. The combined insulation R-value is estimated R-50 per Chapter 26 (ASHRAE 2017). The quantity of air leakage and exfiltration from the conditioned space below is estimated to be reduced to a rate of 0.10 CFM per square foot of attic floor area, or 0.21 air changes per hour, based on Chapter 16 Ventilation and Infiltration (ASHRAE 2017).
The closed cell spray foam insulation in combination with cellulose insulation provide many benefits beside energy savings:
1. They perform well under low ambient temperatures comparing with typical fiberglass insulation (which insulation R-value decreases at low ambient temperatures.
2. They can seal the entire attic floor, including areas in attic corners and roof structures.
3. Closed cell spray foam provides an integral air and vapor barrier.
4. Closed cell spray foam can potentially serve as an acoustical barrier.
5. They do not contain harmful additives, such as formaldehyde or other indoor air pollutants.
6. Cellulose insulation can serve as a fire barrier or flame retardant.
EEM Summary. A bin temperature method was used to estimate annual energy savings. The material and labor cost for the recommended projects was evaluated based on manufacturer's quote and previous experience of similar projects. Detail parameters and assumptions are not listed here, rather a summary table of the EEM is presented in Table 2.
An example of HVAC EEM is presented below--replacing constant volume air handling units (AHUs) with variable air volume (VAV) AHUs.
ASHRAE Standard. Chapter 6 of Standard 90.1 is HVAC, in which several sections apply to this EEM:
1. "Controls that can start and stop the system under different time schedules" per section 188.8.131.52.1 automatic shutdown in off-hour controls.
2. "Each cooling system shall include either an air economizer or fluid economizer" per section 6.5.1 economizers. Based on Table 6.5.1-1, all AHUs in this building require air economizers. "Economizer controls shall be capable of and configured to sequence the dampers with the mechanical cooling equipment and shall not be controlled by only mixed-air temperature" per section 184.108.40.206.2 air economizers control signal.
3. "Zone thermostatic controls shall prevent mixing or simultaneously supplying air that has been previously mechanical heated and air that has been previously cooled" per section 6.5.2 simultaneous heating and cooling limitation. It prohibits the design of dual duct systems with hot/cold air mixing in new buildings, additions, and replacement of portions or existing buildings.
4. Chilled water cooling system "shall be designed to vary the supply fan airflow as a function of load" per section 220.127.116.11.1 supply fan airflow control. Additionally, "static pressure set point shall be reset based on the zone requiring the most pressure; i.e., the set point is reset lower until one zone damper is nearly wide open" per section 18.104.22.168.3. "Multiple zone HVAC systems must include controls that automatically reset the supply air temperature in response to representative building loads, or to outdoor air temperature" per section 22.214.171.124. "The required minimum outdoor air rate is the larger of the minimum outdoor air rate or the minimum exhaust air rate required by Standard 62.1" per section 126.96.36.199 ventilation design.
In Standard 62.1, several sections apply to this EEM:
1. The most widely used ventilation calculation is Equation 188.8.131.52 in section 184.108.40.206 breathing zone outdoor airflow of Standard 62.1, which accounts for people-related and area-related ventilation rates. The minimum ventilation rates in breathing zone are determined from Table 220.127.116.11.
2. Demand control ventilation (DCV) "shall be permitted as an optional means of dynamic reset" per section 18.104.22.168. DCV is most cost effective in those spaces that have a high design occupant density but which are not occupied at that density consistently (e.g. lecture halls). And the most prevalent method of controlling DCV systems is by using the measurement of carbon dioxide (CO2) concentrations.
Based on the comfort zone psychrometric chart from Figure 5.3.1 in Standard 55, space thermal environmental conditions are determined (i.e. 68 [degrees]F and 50% RH in heating, 72 [degrees]F and 50% RH in heating). For this EEM, average air temperature is used in place of operative temperature per Appendix A of Standard 55 and Chapter 9 (Thermal Comfort) of 2017 ASHRAE Handbook Fundamentals.
Existing Condition. A lecture center on a university campus in climate zone 5A was originally constructed in 1960s. It consists of about 20 lecture halls, as well as the concourse areas and supporting spaces. The building is served by 17 AHUs located in various mechanical rooms throughout the building.
2 large AHUs are constant volume dual duct systems with carriable frequency drives (VFDs) on supply fans that are currently used for soft start only. Chilled and hot water coils are in fair conditions. The 2 AHUs are operating based on BAS schedules, they use original pneumatic controls and obsolete legacy direct digital controls (DDC). Such dual duct systems in the building are less energy efficient and less effective in controlling space conditions than other air systems due to the followings:
1. Constant volume fan operation.
2. Simultaneous heating and cooling (mixing hot and cold air flows).
3. High fan static pressure.
4. No feedback from pneumatic zone temperature sensors to building automation system (BAS).
5. No feedback from damper position or zone air flows to BAS.
6. Ineffective control of dual duct boxes with pneumatic damper actuators.
7. No fan controls to balance supply air with return and building exhaust air.
Similar to the 2 dual duct AHUs, the other 2 multi-zone and 13 single-zone AHUs are operating as constant volume systems based on BAS schedules, with pneumatic and obsolete DDC, and with chilled and hot water coils. Table 3 summarizes the combined schedule for AHU supply fans and return fans.
Recommendation. Considering the existing AHU conditions and this EEM likely being undertaken as part of an overall renovation project of the lecture center, it is recommended to replace the existing 17 constant volume AHUs with VAV AHUs instead of retrofitting in place. Therefore, for this EEM the following major tasks are proposed in the scope:
1. Replacing the 2 large constant volume dual duct AHUs with VAV AHUs.
2. Replacing the 2 constant volume multi-zone AHUs with VAV AHUs.
3. Replacing the 13 constant volume single-zone AHUs with VAV AHUs.
4. Replacing pneumatic dual duct mixing boxes (including other pneumatic controlled equipment) with VAV boxes with DDC controls (including sensors in the boxes and at the spaces).
5. Replacing ductwork and diffusers--based on the age and the conditions (including liner material).
6. Incorporate DCV in individual lecture halls using space C[O.sub.2] sensors.
7. Incorporate economizer controls configured to sequence the dampers with the mechanical cooling equipment for free cooling.
8. Incorporate control sequence as a function of load for chilled water control valves.
9. Incorporate static pressure reset control sequence for supply fans in the 4 AHUs.
10. Incorporate supply air temperature reset in response to space load and occupancy-based scheduling.
11. DDC integration for the building with campus BAS.
12. Air system balancing and testing.
Other implementation considerations for this EEM are documented but not listed here, such as EEMs for central heating/cooling systems and campus BAS, hazardous materials (asbestos-containing materials identified in piping insulation, ductwork insulation, flooring and doors) and survey, construction phasing plans, temporary rental services for heating and cooling, and implementation in other buildings on campus.
EEM Summary. A bin temperature method was used to estimate annual energy savings, which include sperate calculations for heating energy, cooling energy, AHU supply fan energy and return fan energy. The material and labor cost for the recommended projects was evaluated based on manufacturer's quote, RS Means, and previous experience of similar projects. Detail parameters and assumptions are not listed here, rather a summary table of the EEM is presented in Table 4.
Despite of the long simple payback period in the lecture center building, the university prioritized this EEM because similar projects already implemented in other buildings on campus demonstrated significant energy savings and the EEM can be widely applied throughout the campus.
An example of HVAC EEM is presented below--retrofitting constant volume kitchen exhaust systems with DCV systems.
ASHRAE Standard. Chapter 6 of Standard 90.1 is HVAC, in which section 22.214.171.124 kitchen exhaust systems apply to this EEM:
1. Table 126.96.36.199.2 in section 188.8.131.52.2 specifies the maximum net exhaust flow rate "if a kitchen/dinning facility has a total kitchen hood exhaust airflow rate greater than 5,000 cfm". The dining building includes one double island exhaust hood and one wall-mounted canopy exhaust hood, the existing exhaust flow rate (constant flow) exceeds the maximum limit from Table 184.108.40.206.2, while the proposed average exhaust flow rate from kitchen DCV stays within the maximum limit.
2. Section 220.127.116.11.3 provides three options for kitchen exhaust system "if a kitchen/dinning facility has a total kitchen hood exhaust airflow rate greater than 5,000 cfm".
a. Option 1: transfer air.
b. Option 2: DCV. This EEM focuses on this option only.
c. Option 3: sensible heat recovery.
3. In section 18.104.22.168.4 performance testing, where kitchen DCV systems are utilized, "additional performance testing shall be required to demonstrate proper capture and containment at minimum airflow.
In Standard 62.1, several sections apply to this EEM:
1. The minimum ventilation rates in breathing zone from Table 22.214.171.124 requires 7.5 cfm/person and 0.12 cfm/[ft.sup.2] for kitchen (cooking) space. The ventilation requirement was verified with existing and proposed kitchen ventilation systems (make-up air unit).
2. The minimum exhaust rates from Table 6.5 requires 0.7 cfm//[ft.sup.2] for kitchen (commercial) space. The exhaust requirement was verified with existing and proposed kitchen exhaust systems.
In general, Standard 55 covers comfort criteria for human occupancy, the same comfort zone psychrometric chart from Figure 5.3.1 applies to commercial kitchens because they are occupied spaces. However, due to highly non-uniform thermal environment in cooking zone and breathing zone in kitchen, some argue the general evaluation criteria for thermal comfort often used in office environments cannot be applied in commercial kitchens and establishing a method for assessing the acceptable working environments in kitchens is necessary (Simone at al. 2013). Therefore, this EEM only uses an acceptable average air temperature in the kitchen space for energy savings calculation.
Existing Condition. A dinning building on an institutional campus in climate zone 6A was originally constructed in 1920s. It includes a commercial kitchen, dining facilities, community room, and offices.
The commercial kitchen is served by two constant volume exhaust hoods (one double island exhaust hood and one wall-mounted canopy exhaust hood) and one constant volume make-up AHU (with a steam heating coil provided by a campus-wide steam distribution system from the No. 2 fuel oil steam boilers in the central plant). Air transfer for make-up air from adjacent spaces is negligible and thus not considered for the energy savings calculations of this EEM. The kitchen generally operates from 6 am to 7 pm, seven days a week. Table 5 summarizes the supply and exhaust fans, and existing supply and exhaust air flow rates. Note that the proposed supply and exhaust air flow rates in Table 5 are the average of annual supply and exhaust operations.
Recommendation. This EEM recommends kitchen DCV control system through installing VFDs on the make-up AHU supply and the two exhaust hood fans, including sensors, controllers, cabling, as well as system commissioning (performance testing per section 126.96.36.199.4 in Standard 90.1) and personnel training. A kitchen DCV uses a light beam and a photo detector to detect the presence of smoke therefore cooking activity. It also provides a temperature sensor on the exhaust air stream to detect heat. On detection of smoke or heat, the exhaust fan speeds up gradually. The make-up AHU supply fan is controlled by the system controller to track exhaust air flow (no cooling is proposed in this EEM based on the existing system conditions and the owner's preference).
EEM Summary. A bin temperature method was used to estimate annual energy savings. The material and labor cost for the recommended projects was evaluated based on manufacturer's quote and previous experience of similar projects. Detail parameters and assumptions are not listed here, rather a summary table of the EEM is presented in Table 6. Note that the fuel oil price is market driven and was declined substantially at the time of the analysis, the No. 2 fuel oil price was based on website information from New York State Office of General Services.
Energy, indoor air quality, and thermal comfort are three most important topics in ASHRAE that have fundamental impacts in HVAC&R industry. The examples of the EEMs are presented to explain the convergence of Standard 90.1, 62.1 and 55 without any necessary comprise in one or another--to provide acceptable indoor air quality and thermal environmental conditions for human occupancy while optimizing energy efficiency in built environment.
The EEM examples presented in this paper do not reflect the results of any specific projects, rather the numbers in the EEM tables are rounded to present the general energy and cost savings based on the author's experience for the purpose of explaining energy efficiency through the usage of the ASHRAE standards.
ASHRAE 90.1. 2016. Energy Standard for Buildings Except Low-Rise Residential Buildings. Atlanta: ASHRAE.
ASHRAE 62.1. 2016. Ventilation for Acceptable Indoor Air Quality. Atlanta: ASHRAE.
ASHRAE 55. 2013. Thermal Environmental Conditions for Human Occupancy. Atlanta: ASHRAE.
ASHRAE. 2017. ASHRAE Handbook--Fundamentals. Atlanta: ASHRAE.
Hunn, B.D. 2010. Theoretical analysis of solar heat gain through insulating glass with inside shading. ASHRAE Journal 52(3):36, 46.
Simone, A. 2013. Thermal comfort in commercial kitchen (RP-1469: Procedure and physical measurements (Part 1). HVAC&R Research 19: 1001-15.
Chonghui Liu, PE, CEM, LEED AP
Table 1. ASHRAE Standard 90.1, 62.1 and 55 Comparison ASHRAE Standard 90.1 62.1 Standard for Energy Indoor Air Quality Standard covers * Building envelope HVAC ventilation (Ch 5), * HVAC (Ch 6), * Service water heating (Ch 7), * Power (Ch 8), * Lighting (Ch 9), * Other equipment (Ch 10). Compliance path(s) * Prescriptive, Prescriptive * Energy cost budget, * Performance rating method. Used mainly by * Architects, * Engineers, * Engineers (design, * Researchers. energy, commissioning), * Equipment manufacturers. Section(s) most used Minimum equipment Minimum ventilation (by engineers) efficiency tables rates tables in Chapter 6 Adopted by IECC IMC ASHRAE Standard 55 Standard for Thermal Comfort Standard covers Human occupancy Compliance path(s) Prescriptive Used mainly by * Engineers, * Researchers. Section(s) most used Comfort zone (by engineers) psychrometric charts Adopted by -- Table 2. Building Envelope EEM--Attic Roof Insulation Value Unit Annual electric 0 kWh/yr energy savings Annual electrical $0 $/yr energy cost savings Annual natural gas 200,000 therm/yr energy savings Annual natural gas $120,600 $/yr energy cost savings Total annual energy $120,600 $/yr cost savings Total project cost $600,000 $ Simple payback 5.0 yr period Life cycle cost $650,000 $ Table 3. AHU Supply Fan and Return Fan Schedule AHU No. Combined SA Combined RA Combined SF Combined RF (CFM) (CFM) Motor (HP) Motor (HP) AHU-1 ~ 2 77,500 62,500 110 17.5 AHU-3 ~ 4 12,500 5,500 15 3 AHU-5 ~ 17 108,000 95,000 117.5 34 Total 198,000 163,000 242.5 54.5 AHU No. AHU Type AHU-1 ~ 2 Dual duct AHU-3 ~ 4 Multi-zone AHU-5 ~ 17 Single-zone Total Table 4. HVAC EEM--VAV AHUs Value Unit Annual electric 560,000 kWh/yr energy savings Annual electrical $43,680 $/yr energy cost savings Annual natural gas 45,000 therm/yr energy savings Annual natural gas $26,928 $/yr energy cost savings Total annual energy $70,608 $/yr cost savings Total project cost 7,500,000 $ Simple payback 106.2 yr period Life cycle cost $10,800,000 $ Table 5. AHU Supply Fan and Return Fan Schedule No. Existing SA & Proposed Average EF Motor SF Motor EA (CFM) SA & EA (CFM) (HP) (HP) Island hood 15,000 9,500 7.5 -- Canopy hood 2 -- Make-up AHU 15,000 9,500 -- 5 No. Type Island hood Double island exhaust hood Canopy hood Wall-mounted canopy exhaust hood Make-up AHU 100% OA make-up AHU Table 6. HVAC EEM--Kitchen DCV Value Unit Annual electric 21,000 kWh/yr energy savings Annual electrical $1,747 $/yr energy cost savings Annual No. 2 fuel 3,500 gal/yr oil energy savings Annual No. 2 fuel $7,000 $/yr oil energy cost savings Total annual energy $8,747 $/yr cost savings Total project cost $52,000 $ Simple payback 5.9 yr period Life cycle cost $67,000 $
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|Date:||Jan 1, 2019|
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