Cutting Energy Costs in Hospitals

You hear a lot these days about sustainable design’s “triple bottom line” of planet, people, and profit. Efficiency is essential to sustaining the successful operation of any energy-intensive facility. How can it be achieved without compromising core function?

09/01/2010


You hear a lot these days about sustainable design’s “triple bottom line” of planet, people, and profit. Make the planet healthy. Make the neighbors like you. Make the bean counters happy. If health care design were to state an equivalent, it might run along the lines of function, reliability, and efficiency: maintain infection control and sustain a healing environment; assure 24/7 utility support; and do so as cheaply as possible without compromising function or reliability.

The overlaps are obvious. Perpetuating long-term healthfulness is immediate to a health organization’s goals, and capitalizing on energy savings is central to its ongoing operations. The tricky part has always been effectively reconciling the potentially divergent means of realizing these purposes. And an incentive even more compelling than self-evidence and institutional mission has emerged: legislation.

What was always a good idea now has a deadline. This article surveys the methodologies and processes of achieving aggressive energy savings requirements, examining a group of strategies and technologies that would be explored to conform to legislation bearing on a specific new hospital project type in North Carolina, and including each option’s estimated first costs, and anticipated energy savin

Coming to a State Near You

The new North Carolina General Statute 143 (Tables 1 and 2) requires that all new state buildings be 30% more efficient then ASHRAE standard 90.1 – 2007. While this expressly applies to a comparatively narrow sector of hospitals, we see it as a desirable benchmark to strive for concerning new facilities. Also, a growing number of hospitals are seeking LEED certification. Since LEED for Healthcare is still in the approval process, we are using LEED Version 3 – New Construction for new hospital facilities. A 30% energy savings results in 10 points as listed under Energy and Atmosphere Credit 1: Optimized Energy Performance. While difficult, this goal is very attainable and helps to achieve certification for our facilities, hopefully even silver or gold status.

Table 1 - Patient Rooms

Table 2 - Exam/Treatment Rooms

 

Code/Standard

 

Outside Air (ACH)

 

Total Air (ACH)

 

Code/Standard

 

Outside Air (ACH)

 

Total Air (ACH)

 

Chapter 13B

 

1

 

2

 

Chapter 13B

 

1

 

2

 

ASHRAE Chapter 7

 

2

 

6

 

ASHRAE Chapter 7

 

2

 

6

 

Tables 1 and 2: Chapter 13B (North Carolina Licensure Guidelines) is the current code in North Carolina regulating required air changes per hour (ACH). Although ASHRAE Chapter 7 is a suggested guideline, the requirements mirror those found in the 2006 FGI Guidelines and have been incorporated into the 2010 FGI Guidelines. Source: NC Licensure Guidelines; 2007 ASHRAE Handbook – HVAC Applications, Chapter 7; ANSI/ASHRAE/ASHE Standard 170-2008

The primary challenges to a healthcare project delineated by the amended statue revolve around meeting the new requirements while maintaining existing state licensure rules and ASHRAE requirements for air change rates, filtration, and room pressurization--all with a finite construction budget. The further degree of project complexity increases early planning efforts, comprehensive project deliverables, and subsequent coordination. And the most encouraging technology for separating air conditioning and air change in in-patient areas, active chilled beam, lacks the precedent of installations in the United States.

The Lay of the Land

For purposes of this discussion, the conceptual example is a proposed campus for an integrated health care system. The proposed campus will include a 250,000-sq-ft hospital, a 50,000-sq-ft medical office building, and a 10,000-sq-ft central utility plant (CUP). The hospital will include a 75 inpatient bed unit and diagnostics and treatment areas, a surgical suite, an outpatient pharmacy, laboratory services, physical and occupational therapy services, and emergency services, including a helicopter pad.

Using the amended statute as a standard, the performance and documentation requirements of energy-efficiency legislation manifest themselves in added rigor. The added complexity is implicit.

Project deliverables are more expansive under the new law, necessitating exhaustive coordination between disciplines and a more integrated approach during the advanced planning (programming) phase. Energy models need to be developed with approved software during the schematic design, design development, and construction document phases. In addition to the base building model, which is a hypothetical code-compliant building, the amended statute requires two options for architectural, lighting, HVAC, and domestic hot water. Both options must demonstrate the energy and water reduction goals, with the lowest life-cycle cost being the determinant. Unlike the U.S. Green Building Council (USGBC) LEED process, the energy-efficiency requirements of the amended statute are based on energy used (BTUs), not the cost of energy. The project team must drive major decision-making early in the process in order to meet the energy conservation strategies. Close collaboration including the owner and all of the design disciplines establishes a method of critical assessment determining the effect that any individual building system design decision will have on every other aspect of the facility. In this way all design decisions are made with the creative understanding of the synergies possible across building systems.

With more strenuous energy goals also comes a third-party commissioning agent requirement. Commissioning must start in schematic design or earlier, and run through initial building operation. Additionally, metering/submetering is required for electricity, natural gas, fuel oil, and water to allow for post-occupancy energy and water reporting. The 12-month reporting period assures that buildings are meeting the conservation goals. If discrepancies exist between actual usage and the targeted energy consumption, causes must be identified and plans for corrective action outlined by the owner.

Passive Strategies

Our conceptual hospital building is being designed to integrate the surrounding conditions of topology, geology, local materials, and local climate/microclimate. The design considers resource and energy efficiency, healthy buildings, and materials to reduce adverse human impacts on the natural environment, while simultaneously improving the quality of life and well-being of occupants and the community.

A well designed, tight envelope is one of the simplest ways to maintain energy efficiency and realize the intended lifespan of the building. By effectively using the building envelope itself, added heating, cooling, lighting, and other energy-intensive systems can be minimized. In instances where active systems appear to be first-cost prohibitive, our team explores passive and manual systems and strategies to meet design and performance goals. The composition of construction elements in the envelope performs functions that can be individually or cumulatively adjusted to respond predictably to environmental variations and to maintain comfort using the least amount of energy.

The team first considers siting and orientation to reduce reliance on electric lighting and regulate solar heat gain appropriate to diurnal and seasonal cycles. Orienting the building to maximize northern exposure and control southern is the most effective method to achieve good daylighting, though care must be taken to control glare from the east and west low-angle sun. A lighting controls system working with the building management system (BMS) can allow for adjustments in electric lights where daylighting is sufficient to perform the tasks required in those spaces. Glazing coatings are becoming more effective and spectrally selective, allowing only visible light and reducing solar heat gain. Glazing percentages and thermal characteristics of different glazing types are considered and modeled.

A growing body of research shows that access to views of the outdoors and nature is an important part of a healing environment. The team examines glazing, façade treatment, and program organization strategies to drive natural light deep into the building. Zoning the building rationally can also help define the massing and orientation, and can play an important role in developing a concept for building services and distribution.

The integrity of the air and vapor barrier is carefully detailed and studied in the energy models. Performance testing of the curtain wall, roof penetrations, and flashing details—as well as the use of thermography—will confirm performance assumptions. The thermal transfer properties of the opaque areas of the façades and roofs will be tested and adjusted where appropriate. Additional R-value here does not necessarily translate into improved energy performance.

Mechanical Systems

Due to air change rate and space pressurization requirements in a healthcare settings, variable air volume systems are effectively ruled out as an energy-saving opportunity. While ASHRAE Chapter 7 of the Application Handbook and ASHRAE Standard 170 do not prohibit the use of variable air volume systems, which is the basis of design for the ASHRAE 90.1 model, the need to maintain space pressure relationships and minimum ventilation rates may necessitate the use of a constant volume system. ASHRAE 90.1 allows the base model to be modified to comply with codes or standards required for the building type, and in this case the design team models both the base and the proposed buildings to comply with ASHRAE Standard 170 for space pressurization, room temperatures, supply rates, and outside air change rates. Comparison of the base and proposed building models indicate neither benefit nor penalty in the prescribed air change rate.

Opportunities for HVAC energy-saving considered for our hospital include:

  • Enthalpy wheels, approximately 60% to 70% heat transfer efficiency, will be used to pre-cool/pre-heat the outside air of the air handling units. By also treating the latent component of the outside airstream, energy savings can be significantly increased compared to a sensible-only heat recovery device, such as a glycol run-around loop or plate heat exchanger. Risk of cross-contamination is minimized by the wheel’s purge to almost insignificant levels.
  • Terminal unit tracking allows airflow decrease in unoccupied spaces to a minimal air change/hour (ACH) while maintaining space pressure relationships. This is possible in areas with predetermined usage schedules, such as operating rooms (ORs). Let’s say our conceptual hospital will have 12 operating rooms and two procedure rooms. During unoccupied hours, the hospital could keep four ORs operational, allowing space airflow to decrease from the required 20 ACH to a minimum 4 ACH. (The terminal units lose accuracy below a minimum percentage.)
  • To provide year-round cooling to our hospital’s main distribution frame (MDF) and intermediate distribution frame (IDF), a heat recovery chiller can be sized to satisfy those loads. Compared to a central utility plant’s centrifugal chillers, the heat recovery chillers are inefficient at approximately 1.1 kW/ton. However, reclaiming the condenser “waste” heat benefits the building heat/reheat systems more than offsets the cooling inefficiency. Additionally, the large main centrifugal chillers are also able to be shut down in the winter months, saving energy and allowing unit maintenance.
  • ASHRAE 90.1 requires boiler efficiency of 80%. We are designing our boiler plant around condensing boilers at 90% efficiency. A disadvantage of the smaller capacity is the need for more boilers. However, this minimizes the required redundant boiler size, making the overall connected boiler horsepower smaller.
  • Domestic hot water heating boilers are now up to 97% efficient, a direct energy savings that represents the second most efficient strategy for our hospital.
  • Variable primary pumping has a lower first cost due to fewer pumps and less piping, thus the resulting energy savings come with no added cost, offering an immediate payback.
  • ASHRAE 90.1 base model requires DX units to serve telecom and electrical rooms. Our proposed alternative is to replace the units with more efficient chilled water fan coil units supplied by the building chilled water system, which is inherently more efficient than DX systems. Care must be taken to avoid running piping over telecom equipment or electrical panels.
  • Active chilled beams allow the sensible and latent space loads to be de-coupled. Unlike a traditional constant volume reheat system, only the ventilation air is cooled/dehumidified and reheated to a neutral temperature. The space sensible load is handled with the cooling and heating coils that are part of the active chilled beam system. Active chilled beams reduce the amount of airflow that must be cooled then reheated from 6 ACH to 2 ACH. The greatest energy savings is in eliminating the reheat for the 4 ACH difference.

While active chilled beams have been implemented extensively in Europe, to date we have not found any hospitals in the United States with active chilled beams installed in in-patient areas. Active chilled beams are modeled for our hospital’s patient rooms, exam/treatment rooms, and administrative areas—only in the bed tower, as specific patient room requirements will not likely change the use of this wing. This will allow approximately 30% of the hospital to be conditioned using active chilled beams. By de-coupling the sensible and latent loads for a space, we can take full advantage of increased envelope construction and decreases in space heat gains, such as more efficient lighting.

Electrical Systems

Opportunities for energy saving in electrical systems include such strategies as the use of more efficient step-down, dry-type transformers, though the greatest gains are to be found through carefully selected lighting controls and lighting power efficiency. Typically, a hospital’s largest energy loads come from the HVAC system, made more efficient with variable frequency drives on the motors and controls systems, and imaging equipment that uses short, high blasts of power that can be difficult to regulate and control. Accordingly, opportunities for electrical energy-saving considered for our hospital include:

  • T-8, 28 W lamps, compared to T-8, 32 W lamps, offer 22% energy savings over the baseline of ASHRAE 90.1, as well as lowest lifecycle cost. T-8, 25 W lamps offer yet further energy savings but light quality suffers, necessitating more fixtures and thus increasing costs and even energy usage.
  • Rather than traditional metal-halide or high-pressure sodium light fixtures, our hospital will use LED-type lighting for exterior areas, with an expected energy savings of 50% for the same level of light output. Projected 70,000-hour lamp life translates to very low lifecycle costs for LED fixtures.
  • Daylight harvesting will be employed in large, windowed spaces. Photo sensors will evaluate natural light levels and dim or brighten supplemental lighting as needed to meet IES recommended levels. Occupancy sensors will be used in periodically unoccupied noncritical areas, replaced by timer switches in such commonly sensor-blocked spaces as mechanical and electrical rooms. Dimming ballasts in corridors will be coupled with photo sensors to adjust light output during the day and with staff controlled manual dimmers to increase nighttime energy efficiency while reinforcing patient diurnal cycles.
  • Our design team also explores the potential savings of highly efficient dry type transformers that step down the 480 V to 120/208 V, reducing “no-load” losses in the form of heat, having a positive impact on the HVAC system as well.

Energy Modeling

The measure of energy modeling required by the amended statute impels a number of early decisions to accurately calculate the proposed energy savings. Wall and roof construction, window and skylight selections, and exterior elevations all need to be completed prior to modeling. Building plans and room arrangements and dimensions need to be finalized for room-by-room energy modeling to accurately calculate the cooling and heating effects of the required supply and outside air change rates, internal loads, and envelope contributions. Even minor changes to the floor plan, or to wall or roof construction, can create setbacks to the energy model schedule.

To isolate each component’s contribution to the overall building efficiency, our team builds the energy model with all of the items that show an energy savings. We then run alternatives, subtracting each component from the model individually. This important—albeit labor-intensive—process allows us to isolate the total energy savings contribution made by each component. It is worth noting that the new statute excludes the receptacle and process load from the energy savings calculation as this is outside of the control of the design team.

The proposed building is an “all air” system, variable air volume (VAV) tracking with reheat down to the prescribed minimum air change rate as listed in ASHRAE Standard 170, that is, 6 ACH for a patient room. Currently we are at 34% energy savings, just above the state-mandated percentage.

Architectural: Due to the required air change rates, the architectural enhancements have no net effect on the overall building efficiency and may actually make the building slightly less efficient because of the reheat necessary to maintain a comfortable space temperature. The less efficient building envelope would in essence give us free reheat throughout the year, while the proposed building at present has to make up reheat. It is worth noting that the “base” energy model included an envelope system that complies with ASHRAE Standard 90.1, which is already very efficient. Improvements to the envelope system in the “proposed” energy model did not result in an energy savings.

Mechanical: The largest savings in the mechanical system prove to be the heat recovery chiller. Cooling efficiency is not as high as compared to the centrifugal chillers, but reclaiming the condenser “waste” heat helps to offset the required reheat due to the prescribed air change rates. The rest of the mechanical savings are modest and range from half a percentage up to just below 6% for the high-efficiency domestic hot water boilers.

Lighting: The prescribed lighting levels listed in ASHRAE 90.1 are already very efficient and difficult to beat. Therefore, we are only showing a 3%-4% energy savings above and beyond ASHRAE.

Active Chilled Beams: A final energy model is performed with active chilled beams in patient rooms, exam/treatment rooms, and offices in the bed tower. The model shows we are at approximately a 36% energy savings over the base 90.1 model with the inclusion of active chilled beams. This is due to moving the required air change rate from the HVAC system to the room, thereby eliminating the need for reheat in the space. Pump energy is increased but will be more than offset by less fan energy.

Common in most hospitals, all-air systems are inherently inefficient—being in reheat mode nearly year-round—and, because of the prescribed air change rates as listed in ASHRAE Standard 170, offset any architectural envelope enhancements. Systems that can decouple the room’s sensible load from the main HVAC system such as active chilled beams or four-pipe fan coil units can take advantage of architectural enhancements to help create a very efficient building by avoiding the required reheat to maintain space comfort conditions typical of an “all air” system.

Energy savings

 

Building consumption  (10-6 Btu/yr)

 

Total energy savings    (10-6 Btu/yr)

 

Percent saved

 

Energy cost per year

 

Savings per year

 

Baseline (90.1)

 

66,849.6

 

 

 

 

 

$1,079,767

 

 

 

Proposed (all air system)

 

43,827.6

 

23,022.00

 

34.44

 

$904,826

 

$174,941

 

 Table 3: Overall building energy saving projection. Source: AEI

 

Component energy savings

 

Component energy savings    (10-6 Btu/yr)

 

Component savings   (%)

 

Component savings per year

 

Component first-cost increase

 

Simple payback (years)

 

Architectural

 

 

 

 

 

 

 

 

 

 

 

Roof

 

58.4

 

0.09

 

$467

 

 

 

 

 

Walls

 

66.5

 

0.10

 

$560

 

 

 

 

 

Glass

 

11.8

 

0.02

 

-$611

 

 

 

 

 

Window shading

 

-136.3

 

-0.20

 

-$379

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Mechanical

 

 

 

 

 

 

 

 

 

 

 

Heat recovery chiller

 

13,471.9

 

20.15

 

$71,688

 

$104,000

 

1.45

 

Condensing boilers

 

216.3

 

0.32

 

$1,353

 

$11,000

 

8.13

 

Air-side economizer

 

1,336.1

 

2.00

 

$23,916

 

$9,000

 

0.38

 

Variable primary pumping

 

1,312.4

 

1.96

 

$23,916

 

Included

 

Immediate

 

Domestic hot water boiler

 

3,918.8

 

5.86

 

$24,508

 

$62,000

 

2.53

 

Chilled water fan coil units in telecom and electrical rooms

 

252.2

 

0.38

 

$6,305

 

Included

 

Immediate

 

 

 

 

 

 

 

 

 

 

 

 

 

Electrical

 

 

 

 

 

 

 

 

 

 

 

Lighting

 

501.2

 

0.75

 

$13,464

 

$90,000

 

6.68

 

Table 4: Individual component contributions to the overall energy savings of the building. This shows the largest energy saving component is the heat recovery chiller. Source: AEI.

Conclusions

The new energy-efficiency requirements of the amended North Carolina General Statute require adjustment to what has been considered the more typical project design delivery. That the ends served by the amended statute differ little from optimal efficiency goals—and are subject to the same absolutes of function and reliability—the legislation itself and its equivalents across the country will ultimately amount to a formality. The distinctions, however, are significa

1.    A truly integrated design approach. This methodology is driven by first principles that push the design process toward solutions that respond to the unique issues of program, bioclimate, and the client’s strategic objectives (where LEED certification pulls the design process toward measures that achieve points). Frequent full team meetings and discussions about systems, strategies, and components to meet the program and the energy-water conservation requirements are essential.

2.    Team education. New energy-efficiency requirements prompt exploration and evaluation of strategies and technologies perhaps not typically installed in hospitals, including enthalpy wheels, active chilled beams, reduced wattage lighting fixtures, and LED lights.

3.    Early modeling. Block loads in schematic design and room-by-room models in design development are necessary to confirm actual overall energy savings as well as savings by each individual design option. This is imperative in making early decisions and providing data to drive project development.

4.    Empirical data support. Running energy models with accurate utility information simplifies decision-making for the owner and design team, helps justify capital project expenditure, and optimizes the energy efficiency of the project.

5.    Front-loaded design and decision-making. Composition and details concerning orientation, massing, wall and roof construction, fenestration, and shading require early determination to allow time to model different energy performance aspects of each component. Modeling is time-intensive. Schedule accordingly!

Any energy-efficiency legislation will almost certainly require that the systems be carefully tracked and that confirmation of the energy savings be documented and reported after 12 months of occupancy. A thorough, high-quality commissioning effort, the inclusion of metering and submetering, and ongoing systems-trending will reap the rewards of a successful, safe, and highly-efficient facility with reduced energy consumption that, ultimately, costs less to operate.

Energy savings

 

Building consumption  (10-6 Btu/yr)

 

Total energy savings    (10-6 Btu/yr)

 

Percent saved

 

Energy cost per year

 

Savings per year

 

Baseline (90.1)

 

66,849.6

 

 

 

 

 

$1,079,767

 

 

 

Active chilled beams

 

42,549.3

 

24,300.30

 

36.35

 

$896,483

 

$183,284

 

 Table 5: Active chilled beam energy savings projection. As active chilled beams have not yet been widely accepted as an energy savings opportunity, we are representing the potential energy savings from ACB's separately from the rest of the items. This shows slightly more than an additional 2% energy savings for the project from ACB's. Note: the ACB energy savings would be greater if a heat recovery chiller was not part of the energy model. We did not want to account for the reheat energy savings twice. Source: AEI.

 

Yanke is the managing principal and healthcare practice leader of Affiliated Engineers’ Phoenix office. Long is the healthcare practice leader of Affiliated Engineers’ North Carolina office.



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