Buildings operation and construction account for more than 40% of emission and 76% of total electricity use in the USA. Healthcare buildings and hospitals in particular, consume 5.5% of commercial buildings energy despite being only 1% of commercial buildings built area. This makes them an good area to target for improvement.
Some of the key metrics to consider when designing a hospital are : EUI, SDA, views, operating CO2, embodied carbon and operating and capital cost. From the operating cost standpoint, according to Target 100, every dollar in profit, equal to $20 of gross income. For a typical hospital in the United States, an energy bill can be between $2-4 Million United States Dollars (USD) depending on the building size and specific locale. A reduction in energy that achieves a 60% reduction suggests an energy savings (convert to profit) of $500,000 - $1,000,000 per year for the typical hospital.
It is essential to identify the factors that contribute the most to the total energy consumption of hospitals so proper design strategies can be implemented.
The following figures illustrate the end-use breakdown for two hospitals.
Looking at the end use break down, it can be concluded that the largest sources of the overall energy use are heating, cooling and ventilation which make hospitals internal load dominated. Reheat is also shown to contribute a large portion of the total energy use. This reheat energy is a result of the central systems cooling incoming air to condition the warmest space in the hospital, typical high plug load internal spaces of the hospital. In order to not overcool all other spaces, of the building the air is reheated locally. Direct energy efficiency design to the heating system is a good starting point strategy for reducing energy consumption of as hospital because of this.
Before jumping into what design strategies can improve the energy efficiency of hospitals, it is essential to identify main design elements that distinguish hospitals from other type of buildings. A key aspect to consider when designing a hospital is room ventilation and air filtration to prevent airborne viruses and bacteria to transfer to other rooms through air stream. ANSI/ASHRAE/ASHE Standard 170-2017, provides requirements for ventilation of health care facilities. This standard specifies the minimum number of air changes (ACH) depending on the space type as well as specifying the type of spaces that require direct exhaust to outside such as anesthesia, emergency room, etc. Following table captures the ventilation design requirements for some of the rooms.
Improvement strategies to reduce energy use and carbon footprint
Reducing the envelope load through proper solar control by adding exterior shading devices. Reducing the envelope load results in lower peak hour solar heat gain and enables the use of smaller and more efficient central plants. This will also reduce the fan power load.
Improving zoning strategies and de-coupling of space tempering and ventilation for most spaces using supplemental radiant sources for heating and cooling rather than fully relying on air-transport for tempering during peak conditions. zonal cooling is achieved by radiant cooling panels providing sensible cooling. Ventilation is done by using a dedicated outdoor air system (DOAS) alongside with dual heat exchanger that handles the latent load as well as part of the sensible load making it a suitable choice for different climates. Hot water panel radiator can be used for zonal heating. Implementing decoupling heating and cooling eliminates overcooling and reheat loads and shift the system emphasis from air to water
Using displacement ventilation to deliver 4 air changes per hour with 100% outside air. This can be done by introduction of cool fresh air into the lower volume of a room at very low air velocities. Heat recovery wheels can be added to the exhaust air system for most spaces except highly regulated rooms such as operating and emergency rooms. Using displacement ventilation alongside DOAS system improve the energy efficiency while meeting the code ventilation requirements.
Reducing the zone loads by reducing the air changes in highly regulated spaces and reducing the plug/lighting load while unoccupied.