From the third quarter 2011 newsletter of the Oregon Association of Professional Energy Managers (Oregon APEM). Used by permission.

The University of Oregon's Lewis Integrative Science Building (LISB), due to be completed in 2012, could be the first LEED-NC v3 laboratory to be awarded LEED Platinum in Oregon and possibly the country. Energy recovery is one of the keys to achieving a LEED Platinum rating. As mechanical engineers for the project, Balzhiser and Hubbard Engineers were tasked with maximizing energy efficiency.

One of our solutions was to use air-to-water heat pumps to capture heat from high-temperature air available year-around in the extensive network of campus steam utility tunnels. Temperatures as high as 130° F have been reported in some sections of the tunnel system during the hot summer months. The recovered heat will be delivered to variable air volume terminal unit heating coils and fan coil units to control temperature in a variety of multi-use laboratories and office spaces. The recovered heat will replace heat typically provided by central plant steam boilers.

The campus has a central boiler plant that generates steam at 60 psi and distributes it to over 75 buildings on campus through a large network of steam tunnels. Even though the steam pipes are insulated, the length of pipes and the high temperature of the steam cause some tunnels to get very warm. The University has recently installed temperature sensors in some tunnels and connected them to their facility management system so that they can trend and study the temperatures over time. This summer they have been recording temperatures as high as 119° F and as low of 96° F. From the University technician's experience they estimate that even in the coldest winter months the temperatures in some tunnels never drop below 80° F. Balzhiser and Hubbard Engineers identified this excess heat as a source of potential energy conservation if it could be converted to useful heat.

The tunnel near the central boiler plant currently has a large exhaust fan that draws air from the steam tunnels and exhausts it to the outside. The tunnels have been extended over the years as new buldings have been added, some tunnels lead directly from the central plant to the buildings, some tunnels connect one building to another. The temperatures vary in the different tunnels, and the airflow between the tunnels also varies. An initial investigation into the airflows has discovered that the airflow direction and velocity varies, and the reason why is not intuitive. The University has decided to conduct further investigation into the airlfow dynamics of the tunnels and is considering adding velocity meters in some tunnels that are connected to the facility management system so that they can better understand the airflow dynamics over time. It is anticipated that by the time the LISB construction is completed, airflow barriers may be installed to help guide the warmest air to the Science Building so that the most heat can be captured by the air source heat pumps.

During the design of the new Science Building Balzhiser and Hubbard Engineers proposed to extract this waste heat and turn it into useful heat. The need to reheat previously cooled air for multi-zone temperature control is one of the largest energy penalties in Science Building HVAC systems. Capturing the waste heat for reheat became a top priority. This will be accomplished by installing three air-to-water heat pumps in the basement mechanical room of the new Science Building with an opening to a branch of the tunnel network. Air will be extracted from this tunnel and exhausted to the outside after passing through three parallel heat pumps. The heat pumps are each sized for 7,500 cfm of airflow and at the manufacturer's rated entering air temperature of 80° F they can lower the air temperature by 26° F. The heat pumps extract heat from the air and inject this heat into a combined water loop. Each heat pump delivers a constant 30 gpm to the water loop which is tied into the main building heating water loop serving the VAV reheat boxes and fan coil units in the building. A steam heat exchanger in the main building loop provides supplemental heat and serves as 100% backup heat should the heat pumps be off line due to maintenance or failure. The heat pump water loop will connect into the building return water piping upstream of the steam heat exchanger to ensure that the heat pumps always provide a baseline source of heat before the heat exchanger is needed. The building automation system varies building loop pump flow, stages the three heat pumps on/off, and coordinates the addition of supplemental heat from the steam heat exchanger to meet building demand on a 24 hour operation basis.

During the winter months when the demand for hot water reheat is the greatest, it is anticipated that the building heating load will be satisfied by delivering approximately 180 gpm of hot water at 140° F.

Even during the summer months reheating of the air in the VAV system is required in many zones for temperature control, and it is anticipated that the building heating load will be satisfied by delivering at least 50 gpm of hot water at 120° F. Consequently it is anticipated that at least two heat pumps will be required to maintain the hot water loop at a 120° F temperature during the warmest summer months.

The manufacturer rates the heat pumps with an integrated Coefficient of Performance (COP) of 7.0 with 80° F entering the heat pump. With the higher tunnel temperatures observed, the COP of the heat pumps will be higher providing a further boost to the heat capture efficiency.

With a total heating output capacity of 816 MBH, the heat pump water heaters will provide a constant and controllable heat supply year-round, using waste energy to reduce central plant boiler demand. Before the heat pumps were added, building-energy modeling performed by Glumac Engineers estimated the reheat energy of the HVAC system to be 35% of the building's total projected energy use. After adding the air-to-water heat pumps, the entire building savings is projected to be 47%, with one-third of the savings attributed to the air-to-water heat pumps harvesting waste heat from the steam tunnels.

Wescor president Jim McKillip, Colmac Industries' Oregon representative, pointed out that the LISB is not unique in having waste heat available for capture. Almost every campus or corporate facility with a common boiler and cooling plant has utility tunnels. These tunnels are typically hot and humid, requiring ventilation air. This is an ideal condition for converting waste energy to usable energy.

"Waste-energy applications are abundant," McKillip said. "For example, every commercial building has exhaust air with significant waste energy. This typically wasted heat can be captured with hydronic heat pumps and used for heating the building and for heating potable water. Heat pump water heaters work well with even low-termperature exhaust air, with COPs of over 3.5 at 55° F and over 2.0 at 15° F. If potable water heating is desired, there are double-wall heat exchangers approved for potable water. The units proposed in this application can heat water up to 160° F in a single pass. Not only is a high-temperature heat pump necessary for heating potable water, but it can also be used for thermal eradication of bio hazards such as legionella."

Other energy saving features incorporated into the building mechanical systems include heat pipe heat reclaim on the laboratory exhaust air systems, variable volume Strobic Air mixed flow exhaust fans controlled to the lowest permissible stack velocities derived from CFD (Computational Fluid Dynamics) wind modeling tests performed on a building model, sash positioner that automatically closes the sash when no activity is detected at the fume hood, unoccupied setback of lab airflows down to as low as 2.4 air changes per hour in labs without fume hoods, chilled beams, and Demand-Controlled Ventilation.

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Dave Knighton is a senior project manager at Balzhiser and Hubbard Engineers. He has worked on a variety of commercial and institutional projects, including: research laboratories, office buildings, hospitals, public safety facilities, schools, museums, and boiler and chiller plants. His specialized focus is HVAC design for research facilities and Direct Digital Control (DDC) building automation systems.

Additional Project Team members: Energy Analysis: Glumac Engineers, Mitch Dec, LEED AP; Mechanical Peer Review: HDR Architecture Inc., Bruce W. Johnson, PE, LEED AP, Principal; Architects: HDR Architecture Inc. and THA Architecture Inc.