March 2, 2015
Roy Gunsolus, AIA ACHA, LEED AP BD+C; Kim S Shinn, PE, LEED Fellow, CxA, BEMP

Is it possible to achieve net zero energy in the healthcare setting, more specifically in a full service hospital?  HKS Architects and TLC Engineering for Architecture recently analyzed this very question in looking at two recently completed green field hospital projects.  Both projects were very sustainably successful in their own right, having achieved LEED Silver and LEED Gold certification respectively.  The first project was a 103 bed hospital (opened 2010) located in Flower Mound, TX; the second was a 90 bed hospital (opened 2013) in Port St. Lucie, FL – both were approximately 200,000 sf.  The supposition we considered was “what if the owner of each facility had charged the design team with achieving net zero energy rather than attaining the highest level of LEED certification possible?" 

  • How could different “passive” design decisions reduce energy consumption?  What are the resultant physical and planning impacts to the project?
  • How could different “active” design decisions reduce energy consumption?  What are the resultant physical and planning impacts to the project?
  • What renewable energy strategies would be needed to achieve net zero/regenerative energy use?  What are the resultant physical and planning impacts to the project?
  • What is the approximate net financial impact of the above to the project?

We first looked at the current state energy consumption/energy use intensity (EUI) for each facility.  The Texas hospital had an EUI of 238, the Florida hospital had an EUI of 149.  Although the projects were located in different climate zones, heating was actually the primary energy consumer for both facilities – both were in hot, fairly humid climates that required significant reheat to overcome the very cool air being introduced as required to meet healthcare’s stringent air change rates.

So, what does it take to get to net zero energy (NZE)?  First and foremost, reduce demand!  The most effective strategies are passive strategies including the following:

  • Sunshades (horizontal and/or vertical)
  • Additional wall and/or roof insulation
  • Optimize building form
  • Optimize building orientation
  • Optimize fenestration/ glazing type
  • Reduce internal loads such as lighting and equipment
  • Passive solar heating

Only after passive strategies have been exhausted and demand reduced as much as possible should active strategies be considered.  These include:

  • Right-size HVAC systems
  • Reduce friction losses (pumps and fans)
  • Increase equipment efficiency
  • Recover waste heat (air or water)
  • Water cooled air delivery such as chilled beams
  • Lower lighting power densities
  • Lighting and occupancy sensors
  • Harvest free energy (daylight harvesting, ventilation cooling)

After exhausting all reasonable passive and active strategies (lean planning principles were instrumental in the design of each facility so the building form was not modified), the EUI for the Texas facility was reduced to 95 and the Florida facility to 112.  These represent significant reductions, but obviously still fall short of Net Zero Energy.  So where do we turn from here?  What makes sense for each facility?

Hospital_03

The final step to achieving net zero energy is to explore viable renewable energy strategies.  We first explored roof top photovoltaic panels.  The Texas facility had a larger footprint (94,000 sf) than the Florida facility (52,000 sf useable as it contained a low roof on the north side), saving an additional 26% as compared to 11% for the Florida hospital.  We also considered covering the surface parking areas with PV “carports”, but this proved to be cost prohibitive.

Microsoft PowerPoint - 2015_0217_NetZeroHospitals_SmartHealthcar

We next looked for district sharing opportunities with proximate symbiotic partners.  We considered wind energy, geothermal, and biogas alternatives with the latter proving to be the most viable practically and financially.  In exploring local opportunities for each facility, a cattle feed operation proved most viable for the Texas facility while a sugar cane bagasse digester was most viable for the Florida facility.

Microsoft PowerPoint - 2015_0217_NetZeroHospitals_SmartHealthcar

Microsoft PowerPoint - 2015_0217_NetZeroHospitals_SmartHealthcar

Obviously these strategies do come with a price tag, they are not free. For both facilities, the chilled beams translated to an initial added cost of about $25,000, but because they used pipes rather than ductwork the floor to floor height was actually reduced about one foot per floor resulting in a net savings of about $60,000.  Building mounted photovoltaic panels resulted in a net add of $4.5M in the Texas facility and $2.5M in Florida.  In both cases the costs associated with a combined heating and power unit and an anaerobic digester added about $8.2M to the overall cost. 

Bottom line, the payback for the Texas facility to achieve net zero energy was about 13.8 years, for Florida it was 9.9 years.  Although the ROI tolerance of most hospital owners is 5 years, it is not totally out of the question for an owner to consider a 10-14 year payback as the lifespan of a typical hospital is usually 40-50 years!  And the good news is that technology is advancing everyday and prices will continue to drop as it becomes more mainstream.

Microsoft PowerPoint - 2015_0217_NetZeroHospitals_SmartHealthcar

Conclusions and recommendations include:

  1. Driving down the EUI requires a major shift away from “all-air” HVAC systems that depend on reheat for temperature control. Consider water-side heat recovery.
  2. Use hydronic systems and radiant heating and cooling systems to take advantage of the greater ability of water to transport energy. Consider chilled beams.
  3. Because inpatient healthcare facilities are 24/7/365 operations, their EUI will always be greater than most commercial buildings.  The practical limit on EUI may only be about 75-80 kBtu/sf/yr  Use process energy control.
  4. Because their energy intensity is so high, it is usually impractical to use building mounted renewable energy sources to provide enough energy generation.  Roof mounted PV is typically less than 25% of energy needs.
  5. District or Cooperative distributed energy generation is a possible solution to the need for greater generation capacity than what building mounted can provide.  Look at the hospital as a community resource.
  6. Partnerships with the community are a logical way to develop these district energy systems.  Consider early planning and outreach.

 

Posted in Green Places, Health