Designing to optimize the whole building is imperative to achieving net-zero goals.
This is reposted from Engineered Systems.
As one of the most energy-intensive facilities in our communities, hospitals require around-the-clock functionality, which means inevitable energy use that often results in elevated and unnoticed consumption. 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.
To reduce operating costs and support sustainability, many hospitals are investing in projects to reduce energy consumption. If a hospital can trim its energy use by 20%, the existing equipment can last longer, and, in the event of an extended utility interruption, it 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.
For a hospital to “first, do no harm,” in the world of health care, the hospital should strive to be a net-zero building.
A typical hospital has a site-based average energy use intensity (EUI) of 235 kBTU per square foot annually, while the average office building EUI is 53. HVAC systems for infection control and comfort account for more than half of that energy. Cooking for patient meal service and on-site cafeterias represents another significant use as well as the lighting, computers, and medical equipment needed to operate 24/7 in the hospital environment. Steam is required to sterilize equipment, which is a significant contributor to energy use.
In rural and urban areas of the country, hospitals spend up to $3-$5 per square foot on energy costs alone. This translates to $7,500-$15,000 in annual energy costs per patient bed. Despite continuous occupancy and requirements for infection control, there are big opportunities for energy efficiency that also lead to cost savings.
To achieve peak efficiency, a net-zero structure requires a comprehensive approach that addresses both sides of energy: the supply side and demand side. Achieving a net-zero rating for hospitals is relatively rare in today’s market and demands rigor and ingenuity. The strategy is to minimize consumption on the demand side first 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 standing buildings to address consumption concerns.
The University of Wisconsin Health (UW Health) is an example of a successful rework of existing health care buildings. The facility saved an estimated $13 million over the last five years by improving energy efficiency by 24%. Focusing on finding ways to make the existing systems work more efficiently, HGA’s retro-commissioning work was defined by improvements in comfort for the occupants and lower energy usage bills. The improvement in energy covered approximately 4.6 million square feet of space across UW Health’s campuses. The integrated health system of the University of Wisconsin-Madison, UW Health, employs 1,400 physicians and 16,500 staff at six hospitals and 80 outpatient sites that serve more than 600,000 patients annually. To help reduce energy costs, UW Health started replacing older equipment with more energy-efficient models, sealing ductwork, and replacing older lights with LED fixtures. Additionally, physicians have led initiatives to reduce energy and waste in the operating rooms.
Some of the measures that were implemented included:
- Scheduling humidification and ventilation systems and only humidifying and ventilating spaces when occupied;
- Turning off overhead lighting during the day, when natural 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 the original design;
- Recalibrating sensors whose accuracy had drifted out of calibration; and
- Adding control sensors to laboratory fan hoods to reduce the amount of air needed when systems are not being used.
For new projects, setting the energy goals early in the process is imperative to efficiency and success. Including firm energy objectives in the RFP phase allows designers and engineers more flexibility and space to create sound, integrated, and calculated plans that utilize and address energy supply and demand.
Building control systems are notorious for being overridden into manual mode in hospitals, essentially bypassing any opportunity for energy savings. Evaluating equipment performance and current space needs allows the systems to be reprogrammed to automatically adjust temperatures and fan speeds, maintaining an optimized patient environment and reducing energy use.
At Allina’s Abbott Northwestern Hospital in Minneapolis, HGA worked with facilities staff to upgrade the existing chiller plant without replacing any major equipment. The chilled water distribution was already capable of variable flow for the secondary loop, but the team identified opportunities for energy savings with minor modifications to distribution piping and controls. Energy savings were realized immediately, and HGA monitored the performance of the chilled water system to set a new baseline for operations. They then used the observed equipment efficiencies to create a new controls sequence to optimize the chiller plant. This approach enabled all equipment to operate within required limits while dispatching equipment and establishing set point strategies that use the least amount of energy to meet hospital demand. Once completed, this project achieved an 18% energy savings with existing equipment, reducing energy use by 570,000 kWh annually.
Decoupling ventilation systems offers another opportunity to reduce the energy demand. Decoupling ventilation from heating/cooling gives the building flexibility to operate by continuously providing fresh 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 also lends itself well to heat recovery systems.
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 that can be met with unique and sustainable supply solutions. 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 everything back to the central plant. Designing to optimize the whole building is imperative to achieving netzero goals. While it is important to be cognizant of the design and requirements of those specialized spaces, the answer is not to lump them all together in terms of energy use.
FIGURE 1 Patient rooms have critical comfort, lighting, and acoustic needs that can still be provided in a net-zero energy hospital building.
Using Net-Zero Strategies for Hospitals 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 carbon impact.
Improving upon the building envelope is an important and complex endeavor. Views are important for patient healing. Shading and details on the facade, as well as materials used, help to reduce the amount of heat gain in the building but can also allow for heat capture when needed. Windows are great for aesthetics and 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. Equipment efficiencies have improved energy performance significantly over the last 20 years, but this equipment is still responsible for 40%-50% of the building’s EUI. Implementing strategies like heat recovery chillers can reduce a hospital’s reliance on a boiler system.
While this application may seem limited, hospitals typically operate chillers year-round and often reheat cooled air in the summer to maintain required indoor conditions. Groundsource heat pumps with closed-loop wellfields offer another strategy for central plant systems to reduce energy use.
No matter how much the demand side is lowered, there is always the need for a supply — and to ensure a strong strategy for a net-zero rating, clean electricity coming in on the supply side is imperative. The supply side can be addressed through on-site and off-site resources. Generating enough onsite renewable energy to meet the demand side is difficult. On-site sources often only account for 10% or less of the energy supply but are worth the investment. Rooftop or ground-mounted solar panels, wind turbines, or bio energy are great options for renewables but are not always a possibility due to space and budgeting constraints. Instead, or in addition to, hospitals often invest in other renewable energy sources, such as participating in community solar gardens or purchasing utility and other renewable energy credits through utility providers or third-party vendors.
Achieving net-zero energy for hospitals is also getting a boost from the increasing “greening” of the national electric grid, as electric utility companies continue to expand their wind and solar generating capacity. Many utility companies have set goals of generating 100% of their electricity from renewable energy sources by 2050.
FIGURE 2 Dashboard data collected from an optimized chiller plant.
Gundersen Health System (GHS) in the Midwest has always had impressive net-zero ambitions and found success investing in a multifaceted solar approach. For GHS’s new Sparta Clinic in Sparta, Wisconsin, operators installed rooftop solar panels that generated up to 100 kW of energy. GHS also invested in a community solar garden by partnering with a local energy provider, accessing an additional 280 kW of energy, reducing costs and allowing the building to achieve net-zero levels.
Combining this action with a geothermal pump system (300 feet deep and utilizing 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.
Gunderson Health’s approach to solar supplied energy wasn’t the only change the hospital system made. Part of Gunderson’s 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 supplied to local homes and businesses. This is due to a holistic approach to the supply and demand sides of energy, a diligent team effort, and commitment to sustainability. Though expensive upfront, their energy efficiency initiatives produced a 60% return on investment. Examples of these initiatives included retrofitting light fixtures, replacing exhaust fans, installing responsive cooling systems, and upgrading appliances to energy-efficient models.
A comprehensive approach involving a variety of methods and tactics is necessary to meet net-zero goals in hospitals. Dissecting energy use on the demand side by considering the needs of specialized spaces as well as the building codes and requirements will lead to a more efficient plan and ease the strain on the supply side.
This article first appeared in Engineered Systems. For more information, visit Engineered Systems.
About the Authors
Manus McDevitt has more than 25 years of experience in energy-efficient HVAC design and engineering systems. He has been extensively involved in the sustainable design industry from early in his career and co-founded Sustainable Engineering Group (SEG) in 2004 (now part of HGA)— a leading engineering firm focused on energy optimization and sustainable design.
Peter Dahl leads sustainable operations across the firm’s core practice groups. His expertise includes sustainable design, LEED consulting services, energy audits, energy modeling, feasibility studies, sustainable master planning, climate action plans, retro-commissioning, and sustainable building rating systems. As a strategic advisor, he works with building owners to evaluate their current energy state and identify sustainable design opportunities to increase energy and resource outcomes.