Underground Piping Systems | P2S

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Kent Peterson

Vice President

PE, ASHRAE Presidential Fellow, LEED AP BD+C, BEAP, MCIBSE

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One of the main components of heating and cooling systems serving multiple buildings such as at a university campus is the distribution or piping network that conveys the energy. The piping is often the most expensive portion of these types of systems. The piping usually consists of a combination of preinsulated and field-insulated pipe in both direct burial and concrete tunnel applications. These thermal utilities must supply sufficient energy at an appropriate temperature and pressure to meet the system heating and cooling needs.

There are many considerations when selecting and designing underground chilled water, heating hot water piping systems that will impact the life and thermal losses of the systems and components selected. This month’s column includes some information for designing underground piping systems.

Utilidors/Tunnels vs. Direct-Buried

A utility tunnel is a passage built underground or aboveground to carry utility lines. Utility tunnels are generally large enough for maintenance access. Utilidors are smaller tunnels typically large enough for only the utility piping. Utilidors are usually connected together with manholes. Underground tunnels and utilidors provide an extra layer of protection for the underground utilities. If utilidors are installed with the tops at grade, they also allow maintenance of utility lines without disrupting the landscaping or streets above.

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The new Student Success Center (SSC) at UC Riverside (UCR) is a 3-story, 62,000 GSF building comprised of general assignment classrooms for modern pedagogies and technology, multi-purpose student life spaces, and dining services. The building is intended to serve as a new beacon on the campus to support student and organizational success through active learning, collaboration, and community building. The project was intended to not only address UCR’s continued student growth and corollary shortfall of instruction space, but to do so in a manner that upholds UCR’s academic mission with an emphasis on reinforcing student success. This project was certified LEED Gold on July 28, 2022.

From a sustainability standpoint, the team coordinated the construction materials to minimize loads within the building and choose climate appropriate solutions. These collaborative efforts allowed the team to minimize the infrastructure and maximize the usable square footage within the proposed footprint. The team worked to analyze every hour of operation to right-size the equipment and provide innovative solutions, some of which had not been utilized on the campus yet. To implement these systems, the team provided examples of where these technologies had been utilized for similar building types and clients. The building also features low-emitting materials that minimize concentrations of chemical contaminants that are damaging to indoor air quality, human health, productivity, and the environment.

Advanced energy modeling techniques were performed to evaluate the impacts of various energy conservation measures (ECMs). The project team evaluated the energy use intensity (EUI) impacts of multiple design strategies and integrated them with cost estimating from the contractor to understand the total benefits of the ECMs. In a number of cases, the team opted to move in a different direction. For those strategies that were employed, we used the following techniques:

-The project has several large lecture halls with occupancy ranging from 100-420 occupants, based on the room size. These lectures hall have high ventilation loads and raised flooring. For these spaces, we used indirect evaporative cooling and displacement ventilation to reduce the demands on compressor driven cooling. These strategies resulted in an EUI savings of approximately 4 btu/SF-year.

- For the large lecture halls, we provided four VAV zones, with the zone controls and reheat coils within the mechanical penthouse. This allowed us to eliminate any service within the space or the raised floor, to minimize the maintenance impacts to the space.

- The campus had an existing steam system that is failing and unreliable. The campus also has a requirement that we cannot have combustion for hydronic heating and domestic hot water. We used a modular heat recovery chiller to generate HHW for the building and export CHW to the campus loop. This strategy had a 7-point EUI reduction compared to the steam system.

- The project utilized a heat pump water heater for domestic hot water.

These solutions would not have been possible without collaboration of the building layout, envelope construction, shading, etc. to minimize the loads seen by the mechanical system. The contractor supported this collaboration by providing valuable input into the cost impacts of the strategies being proposed.