48 AS HRAE Jou rna l ash rae .o rg S e p t e m b e r 2 0 1 1

ASHRAE’s BEST

Valley Hi-North Laguna library uses passive cooling, daylight harvesting, rainwater catchment and

efficient lighting systems to achieve the City of Sacramento’s goal that all of its libraries should be

green buildings. Completed in 2009, the LEED Gold building reduces energy consumption by a predicted

36.9% below ASHRAE/IESNA Standard 90.1-2004 and saves $18,200 in energy costs annually.

The Sacramento, Calif., building is ori-ented 10° clockwise off the east-west axis. This is a design consideration to self-shade the north façade of the primary reading room, the largest space in the project with 40% of the total floor area. Self-shading allows the primary reading room to maximize glazing for daylight harvesting without the need for costly shading devices during the summer’s early evenings. The reading room also uses a sloped roof and ceiling with large, north-facing windows to provide ample, diffuse daylight.

The slope of the roof and higher north-facing windows is a classic method for daylight harvesting, allowing for primar-

ily diffuse daylight to penetrate more deeply into the space than would have been possible with a flat roof and lower window head height.

The roof also is pitched to collect rainwater; the gutter being created by the intersection of the slope of the clerestory and the reading room roof, catching the rainwater as it flows from either side. The integration of all these features in a single roofing system provided cost sav-ings and multi-functional use from the building’s architectural system. Skylights complemented the design to the south of the building, providing additional diffuse overhead daylight in the reading rooms to

the south. Roofing consists of a cool roof coating with high reflectivity.

HVAC innovations included the use of a displacement ventilation system, with-out the requirement for a raised floor, to maximize thermal mass directly in the space. The condenser of the main air handler is evaporatively cooled, and the smaller air handler serving the community room has a heat recovery wheel due to its

library sets exampleBy Jeffrey Blaevoet, P.E., Member ASHRAE; and Chien Si Harriman

About the AuthorsJeffrey Blaevoet, P.E., LEED AP, is a principal and Chien Si Harriman is senior building performance engineer at Guttmann & Blaevoet Consulting Engi-neers in San Francisco.

HONORABLE MENTION: INSTITUTIONAL BUILDINGS, NEW

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Intense Southern Sunlight is Filtered Through Deep Sunscreens

Skylights Allow Limited Direct Sunlight that is Refracted Through Chain Drape

Sunlight Reflects Off Light Colored “Cool Roof” to Interior White Ceiling Lighting Central Spine

Northern Diffused Light Fills the Main Reading Room

Building Integrated PV Laminated to Standing Seam Metal Roof

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Low Velocity Cool Air Enters Low and is Pulled Across the Room

Thermal Mass Walls Give Back “Coolth” or Warmth Depending on Season

Hot Interior Air Naturally Ventilates Out Top of Tower

Rainwater is Funneled with “V” Shaped Roofs to Bioswales in the Landscape

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Figure 1: Integration of sustainable features provides cost savings and multi-functional use from the building’s architectural system.

This article was published in ASHRAE Journal, September 2011. Copyright 2011 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Posted at www.ashrae.org. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information about ASHRAE Journal, visit www.ashrae.org.

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Sep tember 2011 ASHRAE Jou rna l 49

technology award case studies

high ventilation load. A 95% condensing boiler to serve reheat coils also increases overall efficiency. A solar hot water system preheats the building’s domestic hot water.

Thermal mass conditioning is a major innovation feature of this project. Thermal mass was emphasized on this project due to local climatic conditions, and, with the future in mind, given California utilities’ push to use building mass subcooling as a means to reduce peak demand on the elec-tricity grid. Designers endeavored to turn heavy interior mass into a positive feature of the project, as a way to complement the heavy mass of the book stacks, thereby in-creasing the overall interior thermal mass of the project. A unique concrete sandwich wall system and exposed concrete floors were designed to express the mass to the building interior and its occupants, un-obstructed by any architectural features.

The intent of the HVAC designers was to consistently subcool the mass during evenings of the cooling season, to take advantage of Sacramento’s delta breeze, which regularly can cause diurnal swings in outdoor temperature of 30°F (17°C), with nighttime lows regularly reaching the mid-fifties to low-sixties during the summer. Currently, this night-flush of the thermal mass is driven by the building’s supply fans and exhausted by a small fan in a single thermal chimney to assist the air out of the stack in the evenings.

This charged thermal mass can be used in combination with a mixed-mode variable air volume (VAV) displacement system to provide additional comfort at elevated sup-ply air temperatures from the air handler. The thermal mass complements displace-ment/mixed mode by depressing the mean radiant temperature in the space due to the

cold surfaces in the space. This allows the facilities operations staff to test adjustments to the space thermostat setpoint higher than normal, which can further extend the per-formance of the displacement ventilation system in mixed mode with no impact on perceived thermal comfort.

The lighting design used efficient lamp-ing averaging 0.87 W/ft2 (0.08 W/m2). The Standard 90.1-2004 building area method is 1.3 W/ft2 (0.12 W/m2). Lighting loads were minimized by selections of high ef-ficacy lighting fixtures to provide most of the ambient illumination. Lower wattage lamps and fewer total fixtures were needed by using only T8, high color temperature, high CRI lamps selected over lower color temperatures. They provide a perception of brighter spaces with lower total power used.

Occupancy sensors turn off lighting when areas are not in use. Dual-level switching was used in all spaces over 250 ft2 (23 m2) allowing lighting levels to be reduced by 50% in a pattern that allows full function of spaces with reduced power consumption. Lighting installed within 15 linear ft (4.5 linear m) of effective translucent surfaces

Building at a GlanceName: Valley Hi-North Laguna

Library

Location: Sacramento, Calif.

Owner: City of Sacramento

Principal Use: Library

Includes: Teen room, food

court, study rooms, learning

center, computer lab and

classroom

Employees/Occupants: 9/250

Gross Square Footage: 20,300

Substantial Completion: 2009

Figure 2: Interior mass/summer night flush (top). Interior mass/summer daytime cooling (bottom).

Interior Thermal Mass Dissipates

the Day’s Warmth

Hot Air Released Through Top of Tower

Cold Air Brought in to Cool Interior Thermal Mass

Interior Thermal Mass Radiates Cooling

Superinsulated Building Envelope and Sun Shading Protect

from Heat

Evaporative Cooling Used During Peak

Temperature

50 AS HRAE Jou rna l ash rae .o rg S e p t e m b e r 2 0 1 1

(windows and skylights) have separate switching from the rest of the interior spaces allowing lighting to be controlled off when it is not needed. Outdoor lighting used high efficacy fixtures with low-cutoff, allowing the energy to be reduced by nearly 50% below the ASHRAE minimum levels.

So far, the metered electricity (Figure 3) is in line or exceeds expectations, although the natural gas metered (Figure 4) consumption exceeds the simulated consumption. A search for reasons for the anomaly in December is still ongoing as the building continues to be monitored.

Indoor Air QualityASHRAE Standard 62.1 and ASHRAE Stan-

dard 55 were considered essential in the design process. The design used Standard 62.1-2004’s Ventilation Rate Procedure to determine the outdoor ventilation rates of each air handler. The intent of Standard 62.1-2004 was more difficult to meet in heating mode, because of the heated air being delivered at the floor and returned at the ceiling level where displacement is being used and the use of 90°F (32°C) supply air from the overhead VAV system, respectively.

Since the use of displacement ventilation was a key energy efficiency feature of the project, it did not make economic sense to provide two return paths (ceiling and floor) to increase the ventilation effectiveness of the system, and super insulation of the windows and skylights was not cost effective to reduce the winter sup-ply air temperature; CO2 sensors were added to the central air handlers to allow the outside air dampers to turn down below the target calcu-lated in the Ventilation Rate Procedure. In an effort to overcome the ventilation effectiveness penalty, this proved to be a wise choice given the variability in occupancy in the library and first costs, thereby saving energy despite the poor wintertime ventilation effectiveness.

One space where special attention was given to ventilation effectiveness was the main reading room, where the displace-ment supply air temperature was not raised significantly in the winter time, but instead the envelope loads were handled by a perimeter finned tube convector, allowing the supply air to remain slightly cooler than the space temperature.

The heating and cooling system was designed to maintain 75°F (24°C) in the summer and 70°F (21°C) in the winter time, consistent with common procedures for an air-condi-tioned design and meeting the requirements of ASHRAE Standard 55. Improving and extending the comfort range by night flushing the building to store “coolth” in the wall and *DOE-2 is known as incapable of modeling radiant heat transfer between surfaces, and it is unable to always model thermal mass accurately without adjustments to the custom weighting factors. Other load calculators also tend to deemphasize the role of radiant heat exchange.

floor slabs, and depressing the mean radiant temperature has been initially an untested experiment. To understand the transient behavior of the concrete during the flush cycle, the team looked for software that extended beyond DOE-2 or load calculators.* EnergyPlus has been devel-oped with this transient behavior in mind. The design team ultimately chose to use a similar well-validated tool with a European background because of its calculation engine, user interface, and ability to model PPD and PMV based on Fanger’s comfort models. The simulations were used to test a variety of conditions, wall thicknesses, and nighttime flush control strategies

Figure 3: Simulated vs. metered electricity consumption.

Figure 4: Simulated vs. metered natural gas consumption.

40,000

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0

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Simulated Proposed DesignMetered Data

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Simulated Proposed DesignMetered Data

Metered data unavailable for July.

Metered data unavailable for September.

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52 AS HRAE Jou rna l S e p t e m b e r 2 0 1 1

InnovationSeveral key innovative features have been mentioned, includ-

ing the use of a fairly conventional packaged direct expansion (DX) VAV air handler with a displacement system. This in-novation allows the project to achieve high levels of efficiency through innovative air delivery that extends economizer hours and lowers pressure drop. The evaporatively cooled condenser provides additional cooling savings. Thermal mass has also been explained, and the exploration into alternative software choices, with a validation of the modeling results, is forthcoming. A solar hot water system preheats domestic hot water.

Operations and MaintenanceThe evaporative condenser unit used a chemical free water

treatment system that requires very low maintenance, and also reduces blow down of water. The building maintenance sys-tem installed enabled the city to monitor the system remotely through a wide area network (WAN). A separate dedicated unit is used for the community room for stand-alone, after-hours operation.

Cost EffectivenessThe incremental capital cost of the energy efficiency mea-

sures was approximately $306,400 and the associated annual energy savings is $18,200. The total replacement cost every 20 years of the incremental systems is approximately $34,300. The simple payback for the building systems is 17 years.

Environmental ImpactThe air handlers have been specified with R-410A, which is

not a CFC and is non-ozone depleting. Compared to the Stan-dard 90.1-2004, Appendix G baseline building, the project is expected to save approximately 147,120 kWh/year of electric-ity and 1,730 therms of natural gas, avoiding 127,400 lbs CO2 equivalent emissions annually.

Further Study of Thermal Mass EffectsTo better understand the thermal mass effects on comfort,

controls and energy use, Guttmann & Blaevoet Consulting Engineers helped establish a collaborative team consisting of the Sacramento Municipal Utilities District (SMUD), the City of Sacramento, the UC Berkeley Center for the Built Environ-ment (CBE), Lawrence Berkeley National Labs (LBNL) and Johnson Controls (JCI). The study commenced in June 2011 and will be completed in July 2013.

The purpose of the study is to create a greater understanding of how building technologies can be analyzed and deployed to achieve demand response control algorithms in an existing building, which also has a substantial amount of interior thermal mass. This understanding will be found by experimenting with demand response control algorithms, monitoring the result-ing energy consumption and levels of comfort achieved, and maintaining digital records of the achieved results, some of which will be available for publication to the general public.

Interior view showing custom displacement diffuser (bottom left).

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High mass/multi-function construction.

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