How Hospitals Can Achieve Net-Zero Energy
Hospitals are among the most energy-intensive facilities. Anchors for help and healing, they are a vital foundation for science and life. Large in size and capacity, hospitals address diverse needs that require round-the-clock use. This means inevitable energy use which often results in lofty and overlooked consumption.
Motivated to reduce operating costs and support sustainability goals, hospitals are investing in projects to reduce energy consumption. If a hospital can trim its energy use by 20 percent, the existing equipment can last longer and, in the event of an extended utility interruption, the hospital can help more patients while on emergency power. Reduced energy consumption also avoids emissions from traditional energy sources which cause climate change and have quantifiable health impacts. In the world of healthcare, for a hospital to “first, do no harm,” the hospital should be a net-zero building.
The benefits of net-zero buildings have been proven with residential and light commercial facilities. But with the high energy intensity of a hospital typically located on a restrained site, a net-zero hospital raises new challenges for project design teams. But hospitals have found pathways to a net-zero hospital by considering supply and demand. It’s crucial to understand the strategies required to accomplish this feat.
Approaches to net-zero
The energy utilization index (EUI) is the unit used to measure how much site energy a building uses per year; the typical hospital has an average of 235 EUI (the average office building uses just 53 EUI). More than half of this energy in hospitals is for HVAC systems for infection control and comfort. Cooking for patient meal service and on-site cafeterias represents another significant energy use, as do lighting, computers, and medical equipment needed to operate 24/7 in the hospital environment.
Rural and urban hospitals spend up to $3 to 5 per square foot on energy costs alone. This translates to $7,500 to 15,000 in annual energy costs per patient bed. Despite 24/7 occupancy and infection control requirements, there are opportunities for energy efficiency and cost savings. Energy solutions come in two varieties: the demand side and the supply side.
• The demand side is the on-site consumption and management of energy, that is, the amount of energy a hospital uses day-to-day. Think lighting, ventilation, heating, and cooling systems. In a hospital where care is 24/7/365, the demand for continuous energy is high.
• The supply side is how energy is created, and the ability to fulfill the energy demand. This includes any on-site electric generation (for example, roof-mounted solar panels) or subscribing to a large-scale, community-wide energy generation program.
To achieve a net-zero structure requires a holistic approach addressing both the supply and demand sides of energy. Achieving a net-zero rating for hospitals is rare in the modern market and requires diligence and creativity. The best strategy is to minimize consumption first, on the demand side, and then generate the necessary energy in a clean, renewable way, on the supply side.
Net-zero goals are not limited to new construction — existing hospitals can pursue energy conservation projects on existing buildings to address consumption concerns.
An example of a successful revamp of an older project comes from University of Wisconsin Health (UW Health), the integrated health system of the University of Wisconsin-Madison, which serves more than 600,000 patients each year in the Upper Midwest and beyond with 1,400 physicians and 16,500 staff at six hospitals and 80 outpatient sites. UW Health has saved an estimated $13 million over the last five years by improving energy efficiency by 24 percent. One key strategy has been retrocommissioning, which identified ways to make the existing systems work more efficiently to improve comfort for the occupants and reduce energy usage bills. The improvement in energy covered approximately 4.6 million square feet of space of the UW Health enterprise.
Measures implemented included:
• Scheduling humidification and ventilation systems, and only humidifying and ventilating areas when spaces are occupied by people.
• Turning off overhead lighting during the day, when daylight is available (such as in atrium spaces).
• Using more external air to cool the building when temperatures meet what’s needed inside.
• Rebalancing airflows to spaces where occupancy function had changed from original design.
• Recalibrating sensors whose accuracy had drifted out of calibration.
• Adding control sensors to laboratory fan hoods to reduce the amount of air needed when systems are not being used.
To reduce energy costs, UW Health has also replaced older equipment with more energy-efficient models, sealed ductwork, and replaced older lights with LEDs. Additionally, physicians have led initiatives to reduce energy and waste in the operating rooms.
For new projects, it is important to set the energy goals early on in the process. Including objectives in the RFP phase allows designers and engineers more flexibility and space to create solid, sensible, and applicable plans that utilize and address energy supply and demand.
Building control systems that automatically adjust the heating, cooling, and lighting systems are notorious for being overridden into a manual mode in hospitals, essentially bypassing opportunities for energy savings. By evaluating equipment performance and current space needs, the building controls system can be reprogrammed to automatically adjust temperatures and fan speeds to maintain an optimized patient environment and reduce energy use.
At Allina’s Abbott Northwestern Hospital in Minneapolis, the existing chiller plant was optimized without replacing any major equipment. The hospital’s chilled water distribution was already capable of variable flow for the secondary loop, but opportunities were identified for energy savings with minor modifications to distribution piping and controls. Upon implementation, energy savings were realized immediately, and the performance of the chilled water system was monitored to set a new baseline for operations. The observed equipment efficiencies were then used to create a new controls sequence to optimize the chiller plant. This approach enables all equipment to operate within required limits while dispatching equipment and establishing setpoint strategies that use the least amount of energy to meet hospital demand. Upon completion, this project achieved an 18 percent energy savings with existing equipment, reducing energy use by 570,000 kWh annually.
Another opportunity to reduce the amount of energy demanded is by decoupling ventilation systems. Decoupling ventilation from heating/cooling provides flexibility for the building to operate by constantly providing outside air for ventilation and infection control, and only providing heating or cooling if required by the occupant. Chilled beams and radiant panels are examples of how building systems can heat/cool a space independent of ventilation rates. This strategy lends itself well to heat recovery systems, which essentially moves heat away from spaces that are too hot and instead moves it into spaces that are too cold. In application, a chilled beam system is not supplying “cold” — it is actually removing the “hot” to regulate temperature and reuse the heat where it’s needed.
The building envelope is an important and complicated part of the structure to optimize. Careful use of shading and details on the facade, as well as deliberate choices of materials used, helps to reduce the amount of heat gain in the building but can also allow for heat capture when needed. Windows are great for views but allow a tremendous amount of heat into the building on hot summer days, when cooling systems are running at their peak capacity. Architectural designs that use clear glazing with discretion, to provide the views while also limiting solar gain, are crucial to net-zero buildings. Also referred to as passive design strategies, this approach considers sun angles and shading (interior and exterior) to reduce energy consumption and improve occupant thermal comfort.
The central plant is another major area where actionable tactics can be implemented. A hospital's central plant includes the boilers and chillers that generate the hot and chilled water for distribution throughout the building. Equipment efficiencies have improved energy performance significantly over the last 20 years, but this equipment is still responsible for 40 to 50 percent of the building’s EUI. Using strategies like heat recovery chillers produces both chilled water and hot water, which means the heat recovery chiller can reduce the hospital’s reliance on a boiler system. While this application may seem limited, hospitals typically must operate chillers year-round (even in northern states) and often must re-heat cooled air in the summer to maintain required indoor conditions. Ground source heat pumps with closed-loop wellfields are another strategy for central plant systems to reduce energy use by drawing heat from the ground when the hospital requires more heating in the winter, and storing heat back in the ground during the summer when the hospital requires more cooling.
Hospitals have many specialized spaces — exam rooms, medical offices, laboratories, pharmacies, surgical suites, cafeterias — all with varying needs to meet current codes and standards. Thus, each space has unique energy needs. To design a net-zero capable building, these unique energy needs are evaluated individually and as part of a collection of systems: the energy consuming devices within the room itself, the air handling unit and exhaust fans, and back to the central plant. Designing to optimize the whole building is imperative to achieving net-zero goals. While it is important to be cognizant of the design and requirements of those specialized spaces, the answer isn’t to lump them all together in terms of energy use. Using design tools such as an energy modeling program can help to quantitatively compare the energy use from various design options. These quantifiable results also support the comparative analysis to understand the return-on-investment of different options, helping building owners make better long-term decisions related to lower operational costs and lower carbon impact.
No matter how much we are able to lower the demand side, there is always the need for a supply — and to ensure a pathway to a net-zero rating, we must explore how clean the electrons of the supply side really are. The supply side can be addressed through on-site and off-site resources. It’s difficult, however, to get enough on-site renewable energy to meet the demand side. On-site sources may only account for 10 percent of the energy supply but are worth the investment. Installing rooftop or ground-mounted solar panels, wind turbines, or bio energy (such as fuels made from algae or food waste) are great options for renewables but are not always a possibility due to space and budgeting constraints. Instead of and in addition to these, hospitals often invest in other renewable energy sources like community solar gardens or purchase utility and other renewable energy credits through utility providers or third-party vendors.
A medium size Midwest healthcare with net-zero ambitions found success investing in a multi-faceted solar approach. For its new Sparta Clinic, Gundersen Health installed rooftop solar panels that generated up to 100 kilowatts of energy. The organization also partnered with a local energy provider to invest in a community solar garden, accessing an additional 280 kilowatts of energy, reducing cost and allowing the building to be net-zero energy. This, in addition to a geothermal pump system that is 300 feet deep and utilizes 40 underground wells, an LED lighting system and occupancy sensors, has led to energy savings of tens of thousands of dollars and an increase in energy efficiency.
Gundersen’s approach to solar energy wasn’t the only change the hospital network made. Part of its net-zero ambition was energy independence. The journey began in 2008 and while it doesn’t happen every day, most days the hospital system produces more energy than is needed to operate. The excess clean energy is then supplied to other local homes and businesses. This is because of a holistic approach to supply and demand sides of energy and a diligent team effort and commitment to sustainability. Though expensive upfront, the following initiatives produced a 60 percent return on investment:
• Retrofitting light fixtures.
• Replacing exhaust fans.
• Installing responsive cooling systems.
• Upgrading appliances to energy-efficient models.
While there are a variety of methods and tactics to meet net-zero goals in hospitals, a comprehensive approach is necessary. Truly dissecting the demand side of energy use by considering the needs of specialized spaces as well as building codes and requirements will lead to a more efficient plan and ease the strain on the supply side.
Peter Dahl (PDahl@hga.com), PhD, LEED AP BD+C and O+M, is principal with HGA. He leads sustainable operations across the firm’s core practice groups. Manus McDevitt (MMcDevitt@hga.com), PE, CCP, CPMP, has more than 25 years of experience in energy-efficient HVAC design and engineering systems.