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February 2016


Dispatchable Efficiency for Commercial Air Conditioning

Assessing Variable Speed HVAC products for Residential Use

How to Determine Accurate Relationships Between AHUs and VAVs

The Western Cooling Efficiency Center was established in 2007, alongside our UC Davis partner centers, the Energy Efficiency Center, California Lighting Technology Center, Center for Water-Energy Efficiency and the PHEV Research Center through a grant from the California Clean Energy Fund and in partnership with the California Energy Commission Public Interest Energy Research Program.

WCEC partners with industry stakeholders to stimulate the development of impactful cooling technologies that can enable reduced electrical demand, energy and water consumption in buildings.

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In this month’s newsletter, WCEC drafted a white paper on the wholesale market value of dispatchable efficiency for commercial air conditioning. This paper, and subsequent research is seeking to answer the question: How should one value demand reduction from air conditioning efficiency?

Also in this month’s newsletter is a research paper that details a new method to determine accurate relationships between air handling units and variable air volume boxes in large buildings.

WCEC Project Highlight: How to properly measure performance for variable speed fan and compressors in residential systems.

New working paper on pre-coolers as a dispatchable demand reduction measure: “The wholesale market value of dispatchable efficiency for commercial air conditioning”

DualCool Evaporative pre-cooler from Integrated Comfort is an example pre-cooler technology that could be used as a dispatchable demand reduction to reduce use of peak-power plants and stabilize the grid.

How should we value demand reduction from air conditioning efficiency?

Peak electrical demand in California can be attributed mainly to air conditioning. Although a large shift toward intermittent renewables is also introducing new challenges for dynamic management of the electric grid, the peak requirement for conventional generation in the summertime is projected to remain nearly the same. The economic and environmental costs associated with peak generation are significant. Improvements to the full-load efficiency of air conditioning is one of the most direct means to ease peak demand challenges. To the extent that air conditioning efficiency can be dispatched reliably, these technologies might also provide ancillary services to support reliable grid management.

Air conditioning efficiency offers unique advantages compared to other energy management measures, and should be valued for these specific benefits: It can reduce short term wholesale electricity costs, it can contribute to grid stability, it can defer long term public investments in electricity generation, transmission and distribution infrastructure, and it provides more significant environmental benefits by avoiding operation of more polluting peaking power plants.

One way to recognize this value would be to compensate customers for demand reduction from air conditioning through the wholesale electricity market, as if it were equivalent to the cost of avoided generation. In fact, in 2011 the Federal Energy Regulatory Commission issued an order (FERC 745) that would regulate the wholesale electricity market in a way that enables the direct compensation of demand side resources in this way, as long as demand reduction provides net economic benefits. The directive was fashioned around demand response measures, but we believe that the concept introduces important ideas about how air conditioning efficiency could be valued and controlled.

WCEC is developing research on these issues, and helping industry partners to understand the emerging business opportunities for demand side resources. We’ve developed a working paper to explore the topic, and invite input and feedback from industry and researchers:

The wholesale market value of dispatchable efficiency for commercial air conditioning (Download the paper)

The working paper develops an argument for how demand reduction from air conditioner efficiency ought to be compensated on the wholesale electricity market, and envisions business strategies that could use dispatchable air conditioner efficiency as a substantial peak demand reduction measure. We welcome your input and feedback.

Research Paper details a new method to determine accurate relationships between AHUs and VAVs in large buildings.

In many existing buildings, the Air Handling Units (AHUs) and Variable-Air-Volume (VAV) boxes are controlled independently. Because of this control separation, the AHUs do not shut off first when cooling is no longer needed and thus, the VAV boxes are forced to use their re-heat mode to keep the setpoint--wasting significant energy in the process.

To combat this, building managers need to know the relationship between AHUs and VAV boxes. But in many buildings with hundreds of VAV boxes, the maintenance team first needs to figure out which AHU’s serve which specific VAV boxes. This can be done manually, but it could take hundreds of man hours to determine these variables and identifying all the ductwork that connects them can be problematic. Conventional software techniques that use correlation methods can work, but are simply unreliable. In fact, WCEC’s team used a correlation method in a building with over 400 VAV boxes and the accuracy of the method was roughly 1.5%.

WCEC, in partnership with LBNL have come up with a new method for determining the relationship between specific AHUs and VAV boxes that perturbs the system by changing the temperature of the AHU evaporator coil. This method was tested in a large building with an accuracy rate of roughly 80%. To learn more about this method of detection, read the paper here.
Download the presentation here.

Variable speed fan and compressors in Residential systems: How to properly measure their performance

WCEC engineers building the test apparatus in WCEC's environment chamber

Variable fan speed systems can have the potential to save a significant amount of energy, and are becoming standard on new commercial/industrial HVAC systems. There is currently a push to install variable speed components in residential split systems with the idea that many residential systems are oversized for their load, so adding variable speed drives should reduce the energy consumed by the fan and compressor--and reduce system short cycling. Unfortunately, most of the ductwork for residential systems are installed in an attic that, on hot summer days can reach well over 120 degrees.

With that load on the ductwork, combined with a longer residence time of the conditioned air in the ducts due to part-load cooling, the efficiency of the system will be reduced. Current performance standards for residential systems do not address the relationship between the air conditioning system and the ductwork since, most residential systems either run 100% or not at all. With the introduction of variable speed systems, questions regarding their actual efficiency at part-load will need to be resolved in order to properly determine both their efficacy, and to create accurate performance standards for these types of systems.

WCEC is currently building a test apparatus in our environment chamber to address these relationships, and is working to characterize these systems and ultimately build a performance model that can be used by utilities and policymakers.