Controls, Co-gen and Cooling: Retrocommissioning at UC Santa Cruz

As part of the year-long PG&E Retrocommissioning class, the 20 or so participants and three teachers took a two-day field trip down to UC Santa Cruz. There are three aspects that make UC Santa Cruz a retrocommissioning dream location: a) the very invested and progressive facilities staff, b) the wide variety of complex systems on-site, and c) the campus-wide system interactions. As a bonus, UC Santa Cruz also has a gorgeous campus—small clusters of buildings hidden amongst soaring redwoods and cool, misty air.

Invested Facilities Staff

A facilities department can often take on the guise of a maintenance department, where they are maintaining status quo. But as the saying goes “if you’re not getting better, you’re getting worse”. And so the Physical Plant department has endeavored to continually improve, embracing new tools and technologies even if the learning curve is steep at times. One of these technologies is Daintree Networks lighting controls, an award-winning solution they have been phasing in  throughout the campus. This system allows them to provide multi-level lighting control based on occupancy, daylight, schedules and specific space types. For example, a lab space we saw provided a low level of always-on lighting for safety, as well as aisle-by-aisle occupancy control and daylight control for lighting near windows.

UC Santa Cruz has also been implementing new Direct Digital Control (DDC) systems for their existing equipment using the Tridium framework. Unlike many proprietary control systems, Tridium can integrate all of their existing and diverse systems into a unified platform. This has required hours of programming for each building, but the benefits have been immediate—improved control over their buildings as well as monitoring for ongoing improvements.

Complex On-Site Systems

UC Santa Cruz has a co-generation system, and visiting this was what I’d consider a rare and exciting opportunity. The co-generation engine is actually an old naval ship engine that generates energy from natural gas and recuperates waste heat. The waste heat is distributed throughout the campus, replacing the need for boilers to run. With this low-carbon source of heat, absorption chillers are strategically used in place of typical electric chillers.

Co-generation systems are often more efficient than using grid electricity because of higher generation efficiencies (40 - 43% vs ~33%), eliminated distribution losses (which can be 15%) and utilization of waste heat, increasing total efficiency from around 25% to 80% or higher. There are some downsides such as additional maintenance and reliance on combustion. However, for UC Santa Cruz, the co-gen also provides invaluable back-up electricity in the event of a grid black-out.

Being in the co-gen room feels akin to being inside a dog kennel with an elephant and it’s easy to imagine that you’re below deck in an engine room. The picture above is of the co-gen unit—or at least the portion that fit in the frame. You can see the reciprocating engine, with the exhaust to the left. The motor (electricity generator) is to the right outside the frame.

UC Santa Cruz isn’t the only campus with co-gen, and in fact, there are many California universities with co-gen. One of these is Stanford, which has determined that they can reduce their carbon footprint by removing their co-gen and instead implementing green power purchasing. Their decision contrasts sharply to UC Santa Cruz, where they are planning on investing in an upgraded system. The details of this comparison (which I won’t get into here) highlight the multitude of factors that determine feasibility, including natural gas utility rates, electricity utility rates, time-of-use charges, demand for waste heat, maintenance costs and expertise, electricity supply reliability, load profiles, incentives and carbon reduction policies. In the end, there’s no single answer for every building or campus; you need an analysis that takes into account these factors (and more).

At UC Santa Cruz, they’ve decided to circulate the waste heat from the cogeneration engine around the campus as centralized heating hot water. Although this hot water can be used for heating in the cooler months, when it’s warm there’s no need for heat. So when the cogeneration engines aren’t running or aren’t generating enough heat, central boilers run to provide heat.

System Interactions

As a campus, there are innumerable interactions which cause exponential headaches and difficulties. Occasionally, these interactions are valuable opportunities waiting to be exploited. One such opportunity that has been implemented by UC Santa Cruz is a free cooling cycle, similar but different to a traditional water-side economizer. In a traditional water-side economizer, when the cooling tower is generating sufficient evaporative cooling, the chiller compression cycle is turned off. With the pumps running, the chiller is effectively turned into a large heat exchanger, taking the cool from the cooling tower and passively transferring it to the chilled water loop for the building.

At UC Santa Cruz, there is a chilled water plant consisting of three large chillers serving a mini-district of six buildings. There is always a load/call for cooling on this chilled water plant. One of the buildings in the “mini-district” has lab air handling units (i.e. 100% outside air and always on) that supply air between 62 and 67º F. If the outdoor air temperature is below 55º F, the chilled water to these lab AHUs would normally be turned off. However, they have figured out that if they leave the chilled water on at 100%, the outdoor air moving through the air handler will cool the chilled water. This cooling is sufficient that they can completely turn off the 120–600 ton chillers. This varies from a traditional water-side economizer in that the “economizing”, or free-cooling, is taking place in the chilled water loop, rather than the condenser water loop.

In theory and practice, this isn’t a complex system. What I think is cool is that they not only thought of it, but also implemented it. Typically, retro-commissioning measures help buildings better meet the original design intent. In this case they are improving on the original design intent in a way that would have been difficult, but not impossible, to do in design stage.

Don’t let the easy-going atmosphere of the campus fool you—there’s a lot of exciting engineering facilities work happening at UC Santa Cruz. The extended field trip was an invaluable part of the retro-commissioning class. For perspective, I only reported on a fraction of our field trip in this blog. For the rest, you’ll have to join the Retrocommissioning class 2014–2015! The first class kicks off August 8 in San Francisco; learn more about that at Pacific Energy Center’s class calendar.

Thanks to Patrick, Mike, Sarah, Ryan, David and Arik for making the site-visit happen.