To: Scott Dimetrosky, EEB Evaluation Consultant
From: Matt Rusteika, Zack Tyler, & Tom Mauldin, NMR Group
Date: September 17, 2014
Re: R67: Residential Lighting Interactive Effects Memo
This memo details the findings of the Lighting Interactive Effects analysis which NMR Group, Inc. conducted for the Connecticut Energy Efficiency Board (EEB).
Summary of Results
Compact fluorescent light bulbs (CFLs) and light-emitting diodes (LEDs) emit substantially less heat than incandescent bulbs because they convert a much larger percentage of the energy used into light. For this reason, replacing incandescent bulbs with more efficient bulbs results in a small but real impact on the amount of energy consumed by heating, ventilation, and air-conditioning (HVAC) systems. This is referred to as interactive effects (IE). Failure to take these interactive effects into account can lead to inaccurate estimation of savings from lighting retrofits.
Four separate analyses were conducted as part of this study to measure interactive effects in Connecticut residential units. Table summarizes the results of each IE factor analysis.
Table : Interactive Effect Factors Summary
a Proportionally weighted to reflect statewide saturation percentage
of ducted central air conditioning systems—see Section .
b Weighted with heating fuel proportional weight—see Section .
c In BTU/kWh.
d Includes only sites that heat primarily with natural gas.
Each analysis calculates a different factor with which lighting retrofit savings can be adjusted to account for the changes in heating and cooling usage that result from the installation of efficient lighting. REM/Rate™1 energy models initially developed for the Connecticut Weatherization Baseline Assessment2 were used to simulate these interactive effects.
The electric energy analysis results in an average electric IE factor of 1.04. This means that an efficient lighting retrofit in the average Connecticut home will result in 104% of the electric energy savings attributable to the efficient bulbs alone due to interactive effects.
Concurrently, the same retrofit will result in a heating IE factor of 1,902 BTU/kWh. This means that for every kWh saved in lighting, 1,902 BTU in additional annual heating usage will result, on average. This translates to about 0.07 MMBtu annually per bulb, or 1.8 MMBtu annually from a 25-bulb retrofit (the maximum number of efficient bulbs installed through the Home Energy Solutions (HES) program). The heating IE factor applies only to homes that heat with a fuel other than electricity, because heating system interactive effects for electric-heated homes are captured in the electric IE factors.
The analysis also results in a gas takeback factor of 0.56. This means that for the average gas-heated single-family home in Connecticut, 56% of the energy saved by installing more efficient bulbs is negated by the increase in gas heating requirements. The gas takeback factor is essentially the same as the heating IE factor, except that it is unitless and applies only to gas homes. Because it equates electricity and gas, it is best viewed as a way to contextualize interactive effects rather than measure them. It is included in this study because it is a common method of describing interactive effects for gas-heated homes.
About ninety percent of the energy consumed by incandescent light bulbs is given off as heat. More efficient CFLs and light emitting diodes (LEDs) emit substantially less heat because they convert a much larger percentage of the energy they use into light. For this reason, replacing incandescent bulbs with more efficient CFLs or LEDs results in a small but real impact on the amount of energy consumed by HVAC systems. This is referred to as interactive effects. Failure to take these effects into account can lead to inaccurate estimation of savings from lighting retrofits.
NMR used the REM/Rate models that were developed for the Connecticut Weatherization Baseline Assessment to calculate lighting IE factors for single-family homes in Connecticut. Four types of interactive effects factor were assessed.
An electric energy IE factor greater than 1.0 indicates that there are additional electric savings due to the lighting retrofit beyond the savings at the lighting end use, while a factor less than 1.0 indicates that interactive effects lead to a decrease in the expected savings from the lighting retrofit. Program electric savings are multiplied by this factor to adjust for the electric energy interactive effects of lighting retrofits. The electric demand IE factor is interpreted in the same way.
The heating fuel IE factor is expressed in BTU (or heating fuel units such as gallons of oil) per kWh of lighting savings. A positive value indicates an increase in fuel use for heating. This equation is not fuel-specific, and therefore it can be used to determine heating fuel IE factors for all non-electric fuels.
Finally, the gas takeback factor is commonly used to adjust lighting savings in gas homes specifically. Like the electric IE factor, it is unitless—kWh in lighting savings are converted to ccf3 of natural gas. The gas takeback factor represents the proportion of lighting savings that are negated due to increased gas consumption. For example, a factor of 0.5 would indicate that 50% of lighting energy savings at a given home, or due to a given program, are negated by the increase in heating requirements.
Examples of how to adjust savings to account for interactive effects using these factors can be found in .