Moving Towards Net Zero
Buildings consume more than 30% of the total energy produced in North America, including 70% of the electricity. Hospitals, with their high ventilation rates and round the clock occupancy, consume more energy than almost any other building...
Buildings consume more than 30% of the total energy produced in North America, including 70% of the electricity. Hospitals, with their high ventilation rates and round the clock occupancy, consume more energy than almost any other building type. Therefore they are the ideal vehicle for exploring energy efficiency strategies.
For almost the last 10 years, Stantec’s architects and engineers have been involved in research into innovative healthcare design, looking at ways of improving the design of facilities in terms of both their delivery of healthcare and their consumption of operating energy. Stantec has been conducting this research with various research partners such as M+NLB consultants and BTY Group through the Sextant research organization, Purdue University, Cambridge University, and with the help of funding partners such as Kaiser Permanente, BC Hydro, Boston Health and Fraser Health.
Very early on in the research it was determined that hospitals had to be designed using a fully integrated multidisciplinary design approach. It was also decided that their operating energy had to be minimized as much as possible before applying any renewable energy strategies. This understanding triggered research into optimizing hospital ventilation rates and indoor air quality, which was published in 2010 and ultimately resulted in changes to the ASHRAE healthcare standard 170.1.1
The most recent research effort is the “Hospital Configuration and Systems Integration for Reduced Energy Use.” The research explores how the integration of multiple systems can result in a significant reduction of energy consumption within a prototypical Pacific Northwest hospital and how to apply those lessons on other building types and in other climatic zones. Using a 50,000-sq.m prototypical acute care hospital, the strategies tested resulted in a 75% improvement over the ASHRAE 90.1 baseline.
Dedicated Vertical Air
Supply to Each Room
The challenge for any integrated design approach is finding the optimal integration of related and unrelated systems without compromising patient and staff safety. The approach must also have a minimal impact on construction costs. The objective of our study is to provide the data to support strategies that can be implemented within the existing regulatory framework and are adaptable to any hospital in the world.
Modern hospitals must achieve operational efficiency and flexibility, enhance communication within and between care teams, and above all be safe for both patients and staff. The prototype hospital developed for this study responds to these imperatives by organizing it into three main blocks — ambulatory care, inpatient, diagnostic — an approach that allows the building systems to be rationalized to the special needs of each block.
Achieving a high level of indoor air quality comes at an energy cost of conditioning the air entering the building from the outside. Given the 24/7 activity at hospitals, this energy cost is higher than almost any other building type.
For this study we provided dedicated vertical supply and exhaust shafts in each patient room, thus eliminating the potential for cross contamination between rooms, as well as eliminating the need for sound dampers and almost all horizontal ductwork and associated crossovers. The approach allowed a lower floor-to-floor height of 3.6 metres, which reduced construction costs and increased daylight penetration into the courtyards.
The concrete floor slabs were made “thermally active” to allow the use of low-grade energy for heating and cooling, and we decoupled the heating and cooling systems from the ventilation system to allow the use of displacement ventilation in non-critical areas. Automatic exterior solar shading is used to avoid cooling loads beyond the capacity of a displacement system and to prevent hot spots on the floor or walls that would divert supply air from the room occupants.
Seismic System as
As the prototype building was initially designed for the Pacific Northwest coastal region which is a seismically active area, a base isolation seismic system was used. The base isolation system supports the whole building on flexible pads to isolate it from ground movements and is located in a 2.5 metre “crawl space” between the entry level and below-grade parking level.
The research team took the opportunity to explore how this costly seismic requirement could be leveraged to further reduce energy consumption. The space functions as a thermal labyrinth, taking advantage of the temperature differential between day and night by storing the energy and using it in a dynamic manner to reduce the overall energy consumption of the hospital.
A research team from Cambridge University used the prototype building model to test the benefits of using water storage tanks as a thermal media in the labyrinth. They developed a new mathematical model to analyze the labyrinth, which comprises a series of insulated water tanks coupled to an inflow plenum in which the air is able to exchange heat through a series of heat exchange tubes.
Using the model, the Cambridge researchers were able to develop the parameters critical to determining the length of pipe for the heat exchanger, water circulation rate, and size of water tanks for winter pre-heating and summer pre-cooling. This approach allows the thermal labyrinth concept to be used in buildings without a base isolation crawlspace.
Summary of Prototype
The prototype building model was developed in Integrated Environmental Solution’s IES Virtual Environment V6.4 energy modeling software. A model based on the prescriptive parameters of ASHRAE standard 90.1-2007 was developed in order to provide a baseline to which proposed strategies could be compared and savings quantified. Simulations for this study were performed using the climatic data of Vancouver.
The simulations performed on the prototype model include:
• high performance energy transfer system using an integrated, whole hospital 4-pipe heat pump distribution system used for energy recovery as well as for moving energy around the building for cooling and heating, minimizing/eliminating most of the tradition reheat energy;
• high performance building envelope with active shading;
• reduced lighting and equipment loads;
• thermally active surfaces and high mass with in-slab radiant heating and cooling;
• thermal labyrinth;
• natural/hybrid ventilation, using displacement ventilation in all non-critical care areas;
• heating and cooling plant reduction/elimination analysis.
Three Most Important Features
The simulated baseline energy use intensity (EUI) of the in-patient tower was found to be 684kWhr/m2 (217 kBtu/ft2/year), which is typical for this type of building use. The simulated proposed design achieved an EUI of 167.5kWhr/m2 (53.1 kBtu/ft2/year) which represents a 75% savings over the baseline model.
The single greatest contributor to this reduction is the elimination of reheat energy resulting from the capture of waste heat.
Next is a significant reduction of fan energy through the use of the thermal labyrinth and natural/hybrid ventilation system.
Third is the reduction of lighting energy from the use of efficient lighting sources and advanced lighting controls.
Applying the Model to
More Extreme Climates
The use of a virtual model of a prototypical hospital makes it easy to perform the same simulation in other locations. For this study the research team analyzed the same systems using climatic data from Edmonton, Alberta and Phoenix, Arizona. We discovered that both received significant benefits from the water tank labyrinth: in Edmonton where both winter pre-heat and summer pre-cooling led to a 718 MWhr/yr benefit, and in Phoenix where summer pre-cooling leads to significant energy savings of 676 MWhr/yr.
Although further research is required, this study has proven that an integrated approach to healthcare facility design can result in significant improvements in energy consumption regardless of climatic zone.
By leveraging Building Information Modeling (BIM) concepts and the power of analytic software design, teams of the future will be able to test their strategies anywhere in the world and compare their results to the code compliant/ baseline design.
Ultimately the work done in this study is but a stepping stone towards the development of a full service carbon neutral, Net Zero energy hospital. Such a hospital might use low-tech strategies such as south-facing trombe walls or evaporative cooling ponds in the courtyards, or advanced technologies such as optimized solar power generation or additional wind power usage. The ultimate vision is to design, construct, and operate facilities that give back as much as they take from the environment. cce
Paul Marmion, P.Eng., Ray Pradinuk, MAIBC, and Klaas Rodenburg, CET are principals with Stantec in Vancouver.
1 See Sagnik Mazumdar, Yanggao Yin, Arash Guity Paul Marmion, Bob Gulick, Qingyan Chen’s, paper published in HVAC&R Research, September 2010 “Impact of Moving Objects on Contaminant Concentration Distributions in an Inpatient Ward with Displacement Ventilation.” The research indicated that prescribed air change rates could be significantly reduced and IAQ improved by using displacement ventilation in the inpatient rooms.
“Zero Energy Buildings: a Critical Look at the Definition.” P. Torcellini, S. Pless, and M. Deru, National Renewable Energy Laboratory; D. Crawley, U.S. Department of Energy, 2006.
The Zero Energy Buildings Database U.S. Department of Energy http://eere.buildinggreen.com/
“Targeting 100! Envisioning the High Performance Hospital: Implications for a New, Low Energy, High Performance Prototype.” Heather Burpee & Joel Loveland. 2010, University of Washington.
Paul Marmion & Ray Pradinuk,
Andy Woods & Nicola Mingnotti,
BP Institute for Multi-phase Flow,
University of Cambridge, England
Alan Short, University of Cambridge School of Architecture, England
Arash Guity, M+ NLB, San Francisco
Steve Hadden, BTY Group, Vancouver
Research funded by: Stantec Research Fund, M+NLB Energy Analysis,
BC Hydro, Fraser Health Authority.