Making Accurate Energy Comparisons for High Performance Building Renovations

Like someone at Christmas, most building owners are understandably eager to open the box of their freshly renovated building and see the present they hoped for - smaller utility bills. But before the paint is even dry and as more high performance buildings come online, many owners and architects, probably many more than would like to admit it, are seeing energy consumption is not as low as they expected, and in many cases is even higher than the building being replaced. So much for the sugar-plums dancing in everyone's heads.

Typical reactions include: Why is there such a disconnect - my energy bill is even higher now than before - didn't I buy a high performance building? Are the systems even working? I though the photovoltaics were going to save me loads of electricity! Unfortunately these reactions often result from a simplified comparison of before and after energy bills, a comparison that is entirely unsuited to the complexity of renovations to become high performance buildings. The complexity and custom nature of renovating an older building and inevitable reprogramming of its use carry with them intrinsic differences that aren't feasible to account for in a simple comparison of energy consumption in the building. Even comparing a newly minted building via an energy model of a comparable 'standard' building carries some risks in this regard, though the comparison (while one half-hypothetical) is a better attempt to compare equally.

Tendencies for Inaccurate Comparison:

The theoretically most accurate and feasible energy consumption comparison is between an energy-modeled base case building and the completed renovation (excluding an ideal best case of two identical building renovations occurring simultaneously with only differences being energy conservation strategies). A comparison that may seem even just as good and much easier, but that is in reality very problematic is to look side-by-side at a building before and after it has been renovated. Many owners look at this situation and throw out the energy modeling, and instead look at their utility bills before the renovation and those after. Many stakeholders, even if objectively knowing that the renovated building will be fully occupied and will function entirely differently than their existing facility, have a hard time accepting higher utility bills when they spent their capital budget on systems and devices that all "save energy". In renovations, this simplified pre- and -post renovation comparison doesn't include many factors, many common ones listed below:

1. Higher-than-anticipated building usage due to greater occupant density, different program components, more visitors, and longer work hours. In one simple way, this means doors and windows are open much more than anticipated, but also means greater cooling loads and higher equipment and computer use. Often buildings that are in line to be upgraded are 'pre-emptively abandoned' - occupants are moved elsewhere in anticipation of the renovation, building maintenance suffers or is eliminated entirely, and system control decreases. This is typically in the few years preceeding the move to the upgraded facility. This period is also the one from which utility information is typically gathered and used for comparison to the new facility because they contain the most recent data. A facility may be 70% occupied pre-move, and systems are maintained to condition only remaining occupied spaces, tending to skew energy consumption downward.

2. Fully-occupied building vs. underutilized older facilities. Aside from the abandonment that sometimes occurs, the existing building is often less-optimally configured due to poor plan efficiency or inadequacy for program requirements due to the age of the facility. While offices may be crammed with employees, entire basements and floors may be occupied with storage or building infrastructure.

3. Learning curve for new systems. Ocupants accustomed to a drafty old building bring that memory to the new building. Rather than adapt to the acceptable temperatures in the new facility, they may constantly 'fiddle' with the thermostat or open windows out of habit. They also may need time to adapt to the response time of systems in the new facility - 'If I turn the thermostat up at 9am my office won't be warm until 11am.' But in the new facility this may take only a few minutes with a more responsive zoned system, so it can lead to much more equipment short-cycling. Occupants may also prefer to set thermostats at their personal preferred temperatures in new facilities because they believe 'it's a new building so I should have 75 degrees all year'. Whereas in the older facility the occupant was accustomed to a broad (perhaps too broad) range of temperatures and used a sweater to compensate for variations. This scenario also results in increased fiddling with thermostats and cycling of mechanical equipment. This can also increase the instance of simultaneous heating and cooling occuring simultaneously in the building.

4. Higher density of plug loads compared to original building. In some older buildings, needed equipment is not installed because the electrical infrastructure will not handle the capacity required. In a new building this equipment is installed, as are many other new devices that may not have been seen as a worthwhile investment in an older facility. While new equipment may consume less energy in use, the number of devices typically increases. These may include computers, servers, copiers, projectors, automated devices, information kiosks, accessories such as cell phones, computer preipherals and others.

5. Code requirements for new buildings require higher building energy demand. Always-on emergency lighting, monitors and sensors, lighting intensities, constant space ventilation for toilet rooms and electrical rooms, lifts and elevators and escalators all combine to increase electrical demand as well as space conditioning demands.

6. Elevators that may be entirely absent in older buildings, especially those being renovated, and they are large energy consumers. Less often considered is the effect of a top-to-bottom building elevator shaft, which can significantly increase air infiltration and thereby space conditioning needs.

7. Current standards of construction tend to demand higher levels of control, automation, and monitoring related to occupancy. Everything from electronic flush sensors, access control systems, security devices and cameras, exterior illumination levels, to automated projectors and screens and window shades all combine to increase the electrical demands of new facilities that are often absent in older buildings.

8. Requirements for control over indoor environment. Older facilities often operated with a 2-pipe or 4-pipe system with few zones. Often those buildings were not air conditioned or humidity controlled. The renovated facility almost certainly has air conditioning and will likely allow user control of heating and cooling in spaces as small as a conference room or individual office. This greater control requires systems that permit small scale modulation as well as overall temperature and humidity control. This typically means a ducted system, which operates with higher energy consumption (fans, reheat coils, etc) in order to provide the level of thermal comfort demanded in new facilites. Utility bills don't account for increased occupant productivity or health that results from better control over these systems; those factors are seldom considered in simplified energy comparisons.

9. Length of commissioning. Even though a building is occupied, that doesn't mean the building is operating at optimum efficiency. It may take a year or more to commission a building properly - the custom nature and complexity of buildings, especially renovations, means there are no out-of-the-box systems that operate perfectly the first time the breaker is flipped on. Ambitious comparisons between the last year of pre-renovation occupancy and the first year post-renovation are one of the least representative comparisons of actual energy consumption, other factors listed in this article aside.

Of the measured listed above, some tend to sort themselves out over time, typically building occupant behavior and system controls through commissioning. The remainder are factors that make pre- and -post comparisons between a building renovated to be high performing nearly impossible. The complexity and custom nature of renovating an older building and inevitable reprogramming of its use carries with it intrinsic differences that aren't feasibly accounted for in a simple comparison of energy consumption in the building.

AGB 7/2005