The size of ASHRAE Standard 90.1 (2019), “Energy Standard for Buildings Except Low-Rise Residential Buildings,” has grown exponentially to a current length of 422 pages as shown in Figure 1. The amount of time required by design engineers to ensure compliance has also increased exponentially. The staffs of authorities having jurisdiction must expand or disregard a sizeable portion of building codes based on the document. The expansion is based on the logic that a complex document with more explicit dictates reduces energy consumption. If the recent past is an indicator, this does not appear to be true.
The Commercial Building Energy Consumption Survey (CBECS) tracks the energy use of buildings according to the period in which the facilities are completed. There was a modest growth in energy use for buildings erected between 1980 and 2007 when the 90.1 standard in effect (1975-2004) was less than 180 pages. Although total energy use in commercial buildings declined by 12.4% between the 2003 and 2012 CBECS, buildings constructed in the 2008-2012 period used more energy than those completed in the previous 27 years (Energy Information Administration [EIA], 2016).
The CBECS preceding 2012 was conducted in 2003, and some insight is gained by looking at changes in this period. Figure 2 indicates the most dramatic improvements were in space heating and lighting. Water heating experienced a less notable reduction in energy consumption. There was an increase in energy use of computers, cooking, refrigeration, and other. This reflects more on the changes in occupant activities rather than building efficiency. These loads would likely add to the cooling energy use while reducing the need for heating. However, the decrease of lighting energy more than offsets these additional internal loads, and the net effect on heating and cooling requirements would be minimal.
The increase in cooling and ventilation energy is unexpected given the page lengths of the Standard 90.1 (2004) HVAC section (24 pages) relative to the envelope (14 pages) and lighting (6 ½ pages) sections. An improvement in cooling energy use should also be anticipated given the steep decline in heating energy. The reduction is likely a result of better building envelopes, increased use of energy recovery equipment, higher equipment efficiencies, and advanced controls. All of these items should also reduce cooling energy.
Figure 3 provides some insight counter to the conventional wisdom that building automation systems (BAS) reduce energy consumption. The average energy use of all commercial buildings was 89.8 kBtu/ft2 in 2003 and 80 kBtu/ft2 in 2012, while those with BAS/control systems consumed more than 25% more at 114 kBtu/ft2 in 2003 and 100 kBtu/ft2 in 2012. A similar result was observed in a 2011 survey of ground-source heat pumps (GSHPs) in commercial buildings. The 20 systems with BAS had an average Energy Star rating of 61 while those controlled with room thermostats had an average rating of 80 (Kavanaugh and Kavanaugh, 2012).
AWESOME RESULTS WITH SIMPLE LIGHTING W/FT2 LIMITS
The good news about ASHRAE 90.1 and the Illuminating Engineering Society (IES) is the lighting energy was reduced dramatically from 18.7 kBtu/ft2 in 2003 to just 8.3 kBtu/ft2 in 2012. This was accomplished with succinct Standard 90.1 lighting sections during this period of 6 pages in 1999, 6 ½ pages in 2004, and 7 pages in 2007. Simple and enforceable dictates are valuable for many reasons. The lighting section sets limits for various building in watts/ft2. Designers have more time to create optimum solutions and be problem-solving engineers rather than merely code compliance officers.
NOT-SO-AWESOME RESULTS WITH EXTENSIVE HVAC SPECIFICATIONS
There are multiple problems with an energy standard that is 422 pages in length. In addition to the greater time resources required of designers and code officials, a lengthy document is more likely to be filled with loopholes. Below are a few that are imbedded in the HVAC section:
1) The effectiveness of reducing the number of energy consuming components is not emphasized — The HVAC section focuses on specifications for individual items rather than treating the building as a system. Designers are allowed an unlimited number of components as long as each one complies with 70 pages of dictates and tables. Minimal consideration is given to system demand and the resulting impact on the electrical grid. Reducing the size and number of components is a very effective method of lowering energy use.
2)The 1999 fan power limit of 1.5 hp/1,000 cfm is very large and has remained the same for 20 years — The 1999 version of ASHRAE 90.1 set the lighting allowable for offices at 1.3 W/ft2. The 2019 version cut this in half (plus a little) to 0.64 W/ft2. In 1999, the allowable fan power was 1.5 hp/1,000 cfm. The 2019 version of ASHRAE 90.1 sets the allowable fan power at “nameplate hp < cfm × 0.0015 for VAV systems” which converts to 1.5 hp/1,000 cfm. This is a lot of power and heat.
Consider a fan with a motor/VSD drive efficiency of 90% and 400 cfm/ton:
W(kW/ton) = 0.746 kW/hp × 400 cfm/ton ×0.0015 hp/cfm ÷ 90% = 0.5 kW/ton.
This power is converted to heat, resulting in a 14% lower net cooling capacity.
qFanHeat = 0.5 kW/ton × 3,412 Btu/kWh = 1,706 Btu/h = 0.14 ton.
3)The allowable fan power is so large, oversized pumps have little impact — The SSPC 90.1 response to a request to establish limits on pump power was, “We toyed with the idea of a transport energy limit similar to the one we have for fans, but the calculation showed that a pump would need some ridiculous amount of head (like 1,000 feet) to be as inefficient at transferring heat as we allow fans to be.” (SSPC 90.1, 2009)
If pump power to match the fan power limit is “ridiculous,” possibly the fan power limit is ridiculous.
In 2010, Table 3-188.8.131.52 was added with water flow rate limits for each “nominal” pipe size. Allowable flow rates for variable-flow/speed systems are 50% higher than flows for “other” systems. Using the same equation widely applied for variable flow power reduction to justify VS drives [W2=W1*(Q2/Q1)3] , the power required to move water through a variable flow piping system would be 337.5% greater than for a constant flow system.
Additionally, the term “nominal” is ill-defined. Consider that 3-inch nominal PEX tubing has an inside diameter of 2.43 inches. An allowable limit for 3-inch piping is 270 gpm, which results in a head loss of 40 feet of water per 100 feet of PEX tubing. This is 10 times the loss recommended in the “ASHRAE Handbook of Fundamentals” (ASHRAE 2017).
Consider a system in which water pumps for the building and chiller have a combined head of 150 feet of water at 2.4 gpm/ton (Δt≈10°F), 70% efficiency pumps, and 85% efficient motors. The resulting power is:
W(kW/ton) = 150 ft. × 2.4 (gpm/ton) × 0.746 kW/hp ÷ 3,960 × 70% × 80% = 0.114 kW/ton
qPumpHeat = 0.114 KW/ton × 3412 Btu/kWh = 390 Btu/h = 0.03 Tons
4)Replacement of Performance Data with Inflated Seasonal/Integrated/Annual Efficiency Ratings — Published ratings at design conditions and efficiencies are being replaced with seasonal, integrated, and annual ratings, such as integrated energy efficiency ratio (IEER), integrated part load value (IPLV), seasonal energy efficiency ratio (SEER), SEER2, combined energy efficiency ratio (CEER), heating seasonal performance factor (HSPF), HSPF2, fan energy index (FEI), fan efficiency grades (FEG), annual fan utilization efficiency (AFUE), heat-induced epitope retrieval (HIER), and simultaneous cooling and heating efficiency (SCHE). None of these can be compared with any of the others without a level of difficulty.
Consider IPLV for an air-cooled chiller. IPLV is found using 1% of the EER at 95°, 42% of the EER at 80°, 45% of the EER at 65°, and 12% of the EER at 55° (Air-Conditioning, Heating & Refrigeration insitute [AHRI] Standard 550/590). Thus, the performance at 55° outdoor temperature has 12 times the impact on IPLV compared to the performance at 95°. ASHRAE 90.1-2019 allows compliance with an IPLV of 16 or an EER of 9.7 at 95° (Table 6.8.1-3). The EER only includes the power to the compressor and condenser fan. The power and heat deduction for the interior fans and pumps must be included to obtain system efficiency.
In 2019, in Phoenix, there were 1,431 hours with outdoor temperatures of >95° of which 378 hours were between 105° and 114° (Weather Underground, 2020).
At an outdoor temperature of 95°F:
WChiller(kW/ton) = 12,000 Btu/ton·h ÷ 9.7 Btu/W·h × 1000 W/kW = 1.24 kW/ton
Adding fan and pump power inputs results in:
WSystem(kW/ton) = 0.5+ 0.114 + 1.24 = 1.85 kW/ton
The net cooling capacity is then corrected by 14% and 3% due to the fan and water pump heat:
WNetSystem(kW/ton) = 1.85 kW/ton ÷ (100% - 17%) = 2.23 kW/ton
The system EER for the air-cooled chiller system for an outdoor temperature of 95° is:
EERSystem@95° = 12,000 Btu/ton·h ÷ 2.23 kW/ton × 1,000 W/kW = 5.4 Btu/Wh
The EER for the chiller would be 8.0 Btu/Wh at 110°. Repeating the above calculations yields:
EERSystem@110° = 12,000 Btu/ton·h ÷ 2.55 kW/ton × 1,000 W/kW = 4.7 Btu/Wh
The system would operate in Phoenix for 1,431 hours per year with EERs between 4.7 and 5.4 Btu/Wh.
5)Dreadful Efficiencies of Small Equipment (even though there are millions of them) — The efficiencies of fans and pumps less than 1 hp are excluded from regulation in the standard (exceptions to Table 184.108.40.206.2). An exhaustive AHRI research project revealed terminal fan efficiencies (wire-to-air) varied between 8% and 36% with electronically commutated motors (ECMs). The efficiencies for fans with permanent split capacitor (PSC) motors varied from 6% to 32% (O’Neal, et. al. 2016).
AN ABSENCE OF MEASURED DATA TO INFORM AND VALIDATE SUCCESS
The CBECS data and Standard 90.1 loopholes presented above are sufficient to question the effectiveness and possibly the validity of ANSI/ASHRAE/IES Standard 90.1. Undoubtedly, the use of additional detailed information would be beneficial; however, ASHRAE and associated organizations have no alternative comprehensive information sources to verify the effectiveness of energy standards.
Without published and verifiable data, developers must rely on computer models to develop the standard. These models must make the following assumptions that are often invalid.
- Electronic controls will function as intended;
- Installation practices will closely follow design documents;
- The equipment maintains advertised performance (i.e., leak free refrigerant circuits, regular maintenance, ratings provided at realistic conditions, etc.);
- Equipment is sized without excessive factors of safety; and
- Detailed equipment performance data and control algorisms are complex and often unavailable, thus “work-arounds” based on seasonal ratings or theoretical relationships are accurate.
In 2009, a well-intended ASHRAE effort to measure and verify performance was initiated. The Building Energy Quotient (bEQ) program intended to “Drive both existing and new buildings toward the net-zero energy building target outlined in ASHRAE’s strategic documents.” Labels with letter grades based on energy performance would inform the public, owners, tenants, and operators of the building’s energy efficiency. The response from the bEQ committee to a November 2015 query was, “Only rated 40 buildings to date, so there is not really much to aggregate at this point. Many of those are not great ratings, so the buildings may not wish to publicize.” (Building Energy Quotient Committee, 2015)
There is no comprehensive ASHRAE program to measure building energy performance and validate the society’s flagship energy standard. In this vacuum, cities and states will begin to establish programs to fulfill this need. New York City has moved to create its own building efficiency label based on the EPA Energy Star program that will also include the EPA numerical (0-100) rating. Building owners will be required to provide a label and rating on buildings larger than 25,000 ft2.
ASHRAE may face a potential loss of credibility when Standard 90.1-compliant buildings begin to receive poor grades. This will certainly happen with air distribution systems requiring 1.5 hp/1,000 cfm, liquid piping with 40 feet of head loss per 100 feet, and propriety equipment controls that communicate poorly with the BAS.
SUMMARY: WHY NOT FOLLOW THE SUCCESS OF LIGHTING POWER DENSITY AND…
Clearly, adjustments are needed to Standard 90.1’s HVAC section. The first step in reducing energy use is to decrease total power input. Sophisticated controls will be unable to effectively offset high electrical demand even if they work as advertised (which they often do not). The simple concept of lighting power density (LPD) has been demonstrated to be very effective. Cooling power densities (CPDs) in W/ft2 (W/m2) could be equally effective. CPDs could be set for each building type listed for LPDs with adjustments for climate zone (Kavanaugh, S. P. et. al. 2006). Although the 2012 CBECS results show favorable heating energy results, the concept could also be extended to building heating mode. This would be more complex in that a correlation between electrical power and fuel rate would be necessary.
…CHALLENGE ARCHITECTS AND CONTROLS PROVIDERS TO BE ACCOUNTABLE
A quality building envelope is critical to minimize HVAC cooling demand and heating requirements. The most efficient mechanical system cannot effectively compensate for an energy intensive building. The Standard 90.1 envelope section is primarily the domain of architects. Recognition of poor envelope energy design only requires accurate cooling load and heat loss calculations. Architects can make buildings beautiful but also be challenged (or required) to minimize the cooling and heating equipment capacity. Cooling heat gain and loss densities (HIDs) can be developed in Btu/h·ft2 (W/m2) for the same building types listed in the lighting section of ASHRAE 90.1. Power and heat rate requirements can be minimized with a combination of quality buildings and efficient equipment.
Building heat gain or loss (Btu/h·ft2) ÷ EERSystem (Btu/W·h) ≡ W/ft2
The remaining challenge is to ensure the equipment controls are functioning properly. Open communication and long-term functionality issues remain largely unresolved. A no better example is the Tullie Circle ASHRAE Headquarters. Even with solar assistance, the first Energy Star rating the building received was a 77. In spite of substantial monetary and personnel resources, the building was not even in the top 20% of peers. ASHRAE, unlike most building owners, had sufficient clout to hold the parties accountable. One of the resolutions is described by the commissioning firm.
“[We] helped to resolve conflicts between [manufacturer] based control system and [main] control system read/write issues that negatively impacted VRF performance, control point crossover issues causing heating and cooling conflicts between adjacent zones, and internal control issues affecting performance of VRF. As a result of [our] findings during the four-year, monitoring-based commissioning process, we were able to provide valuable input to VRF manufacturers’ research department that traveled to the site for review, discussion, and resolution.”
Measurement of energy use, demand, and occupant satisfaction is essential to making controls providers and equipment manufactures accountable for success.
Although the concept of global warming is not universally accepted, it should be noted that bin temperature data based on the 1997 ASHRAE Fundamentals Handbook contained 972 hours for Phoenix in the 97° and above temperature bins (InterEnergy, 1999). As noted in this article, there was a recorded increase to 1,431 hours in these bins in 2019.
- 2012 CBECS: Energy Usage Summary. US Energy Information Administration, 2016.
- Kavanaugh, S. and J. Kavanaugh. 2012. “Long-Term Commercial GSHP Performance, Part 2: Ground Loops, Pumps, Ventilation Air and Controls”. ASHRAE Journal. 54(7).
- Standing Standard Project Committee 90.1, 2009. Electronic-mail Communication.
- ASHRAE 2017. Handbook of Fundamentals, Chapter 22, p.22.27.
- AHRI Standard 550/590 (IP), 2015. Performance Rating of Water-chilling and Heat Pump Water-heating Packages Using the Vapor Compression Cycle. Pp. 10-11, Arlington, VA.
- O’Neal, D.L., Reid, C., Ingram, D., Lu, Di, Bryant, J.A., Gupta, S. Kanaan, B., Bryant. S., and Yin. P. 2016. Developing Fan Power Terminal Unit Performance Data and Models Compatible with Energy Plus, Report NO. 8012, Air-Conditioning, Heating, and Refrigeration Institute, Arlington, VA.
- Building Energy Quotient Committee, 2015. Electronic-mail Communication.
- Weather Underground, 2020. https://www.wunderground.com/history
- Kavanaugh, S. P, S. Lambert, and N. Devin. 2008. “HVAC Power Density: An Alternate Path to Efficiency.” ASHRAE Journal. 48(12).
- ASHRAE Headquarters Renovation, 2008. https://cxgbs.com/ashrae-headquarters-renovation/
- InterEnergy Software. 1999. Bin Maker Plus. Chicago.