Lighting complements a demand-response HVAC system

Here are several reasons that lighting can be a good complement to a demand-response HVAC strategy.


Learning objectives:

  • Learn about how lighting and HVAC are related.

  • Review the impact on electrical consumption as it relates to integrating lighting and HVAC design.

  • Assess how lighting is predictable, linear, and responsive.

Tuning knobs provide an example of how a commercial facility’s fine-tuning demand-response knob can display the lighting system’s predictive, responsive, and linear nature. Courtesy: Hubbell LightingIn 2003, the U.S. Energy Information Administration (EIA) released a Electricity Consumption survey that demonstrated how lighting accounted for 37% or more of all energy used in commercial buildings. This percentage was eye opening for facilities managers responsible for demand-response (DR) or peak demand management (PDM) energy strategies when they found out this was more than HVAC combined. Only when refrigeration was added to the mix did HVAC/R use more electricity.

So the natural question became, why wouldn’t engineers include lighting in a DR strategy?

The prevailing theory found in many facilities was that DR and PDM were climate-driven, so HVAC was at its maximum when DR and PDM were most needed. Lighting used the same amount of energy on a Tuesday in June as a Wednesday in November, which made facilities naturally gravitate toward HVAC for DR and PDM. It wasn’t until consultants began showing the impact on the commercial electric bill that many saw the need for integration.

This changed dramatically in May 2016 when the new 2012 EIA Electricity Consumption survey data was released and demonstrated a large decrease in the amount of electricity used for lighting. Lighting moved from more than 37% down to 17% for an average commercial building. Lighting did its part in energy reduction with the introduction and enforcement of energy codes, reducing lighting power densities (LPDs) and adding more controls.

At the same time, LED adoption was gaining momentum and on its way to becoming the dominant light source with its low-energy, high-output capability. While lighting was decreasing dramatically, the same report had HVAC staying basically the same. In fact, it showed a slight increase to 32% of energy use, marginalizing the contribution of lighting to DR or PDM. This did not bode well for the argument that the overall scale or consumption of lighting warranted facilities to bring lighting into the DR or PDM schema.

So, the natural question emerges: If lighting is not the major energy consumer it was in 2003, then does lighting still have a role in DR and PDM? The short answer is yes.

The long answer says lighting is the perfect stabilizer. Its contribution might have decreased, but it offers significant value in its ability to complement HVAC’s shortcomings. HVAC is only as predictable as the weather and can catch a facility off guard. HVAC’s effect on the built environment is certainly not linear. How long does it take for a thermostat change to make an impact?

Lighting is predictable, linear, and responsive. Additionally, any changes can be nonintrusive, allowing it to counter any energy missteps from a HVAC DR or PDM strategy. Consider how, years ago, a stereo amplifier had a knob for tuning and another knob for fine tuning. The tuning knob would do the basic work of setting the sound. The fine-tuning knob would tweak the sound for optimal performance. Lighting has the potential to now become the commercial facility’s fine-tuning DR knob with its predictive, responsive, and linear nature.

Predictability—Unlike HVAC, lighting is largely shielded from environmental influences. Cloud cover during the day is the only environmental contribution that impacts lighting. Consider how daylighting is only one out of multiple energy saving strategies with lighting along with high-end tuning, scheduling, and occupancy. Energy use for lighting the first Monday in April is going to be identical year to year if the space use has not changed. This is not the case with HVAC, whereas that same day in April might warrant heavy coats or polo shirts.

Responsiveness—Lighting is instantaneous to the human eye. Add current and lights will respond with illumination. Decrease current and so go the lights. HVAC deals with the thermal mass of a building that acts like a freight train. Just as a freight train starts out slow and builds to a steady speed before its inertia makes it difficult to stop, HVAC’s control does the same with the thermal mass and its inertia in a building. It can take hours to recover desired temperature after a DR event. If the recovery is pushed too hard, you can trigger a peak in energy use. Lighting gives that fast response needed for tweaking to counter mistakes from a DR event with HVAC.

Linear—Lighting is linear. Add current and you increase light. When you decrease current, you decrease light proportionally. Providing exact control gives the user knowledge of the outcome for every action in advance. Controlling the thermal mass of a building is not a linear function. It takes time to reach temperature setpoint and then it fluctuates around the setpoint. The linear nature of lighting allows for precise control. That 40% reduction equals a set amount of light, just as that 60% increase equals a set amount of light. This, with productiveness and responsiveness, adds to the full controllability lighting has to counter any mistakes in a DR/PDM program strategy or to make simple tweaks anytime of the day.

Nonintrusive—The human eye works like a camera, increasing or decreasing the aperture and allowing the sensitivity of the human eye to increase light input with the decrease in light intensity. This function is automatic and unperceivable to the user but allows for a decrease or increase in lighting to be unnoticed. Studies by the Lighting Research Center at Rensselaer Polytechnic Institute demonstrate how 80% of subjects accepted up to a 30% or 40% reduction of light and 50% couldn’t even detect a 15% or 20% reduction at all. Add a slow fade of 10 seconds or more, and that number goes up. This means a facility manager can decrease or increase the lighting by 10% to 20% at any time to counter or tweak HVAC DR/PDM measures without a negative impact on tenants.

Lighting is the best complement to HVAC in DR or PDM strategies because of it predictability and ease of management. Sure, it’s now a likely smaller load than HVAC, but being linear over time, responsive, instantaneous, predictable, and unnoticeable makes it the perfect tool for fine tuning DR actions.

Scott Ziegenfus is the manager of government and industry relations at Hubbell Lighting.

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