{"id":13196,"date":"2015-12-09T14:30:47","date_gmt":"2015-12-09T19:30:47","guid":{"rendered":"http:\/\/www.constructionspecifier.com\/?p=13196"},"modified":"2016-12-15T11:36:21","modified_gmt":"2016-12-15T16:36:21","slug":"taking-hvac-performance-beyond-the-baseline-combining-geothermal-doas-and-chilled-beams","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/taking-hvac-performance-beyond-the-baseline-combining-geothermal-doas-and-chilled-beams\/","title":{"rendered":"Taking HVAC performance beyond the baseline: Combining geothermal, DOAS, and chilled beams"},"content":{"rendered":"
\"Davis\"<\/a>
All photos courtesy Anne M. Rissier Lee, University of Findley <\/span><\/figcaption><\/figure>\n

by Thomas Rice
\n<\/strong>As consulting engineers continually specify more sustainable HVAC technologies, they must ensure their designs comply with a variety of standards. Of course, when possible, it is even better to go far beyond those baseline requirements. In this respect, the University of Findlay\u2019s $11 million Davis Building is a role model for future commercial mechanical technology, as it is an example of a facility design exceeding minimum requirements of several American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) standards.<\/p>\n

The 3900-m2<\/sup> (42,000-sf) building, south of Toledo, Ohio, is based on a geothermal concept, but it far surpasses conventional system designs that employ heat pumps or unitary air-handling units (AHUs). Instead, the building employs chilled beams and dedicated outdoor air systems (DOAS) for energy recovery and outdoor air.<\/p>\n

The science facility, which consists of 19 labs, four classrooms, a 112-seat lecture hall, computer lab, and 15 faculty offices, recently won an ASHRAE Technology Award in the Educational Facilities\u2212New Construction category. More importantly, the HVAC system is saving 57 percent more energy, which translates annually into a $59,000 energy savings and $7500 in reduced maintenance. Its energy use intensity (EUI) is only 64 kBtu\/sf.1<\/sup><\/p>\n

The HVAC system was designed by Stephen Hamstra, PE, LEED AP, an ASHRAE-certified High Performance Building Design Professional (HBDP) of consulting engineering firm, Greensleeves. RCM Architects was the building architect.<\/p>\n

Geothermal and chilled beams
\n<\/strong>Typical geothermal systems deliver water pre-conditioned by inherent ground temperatures to forced-air systems such as heat pumps or air-handling units (AHUs). Fan energy is used to distribute air across these systems\u2019 coils.<\/p>\n

Instead of conventional design using heat pumps and air-handlers, the University of Findlay project used ceiling-mounted chilled beams, which are fin-and-tube heat exchangers distributed strategically throughout a room. Therefore, the geothermal water is pumped to chilled beams, which condition the space via convection. Warmer air rises up to the chilled beams and then falls downward as it cools. This results in a less drafty, more evenly tempered space, but most importantly, chilled beams boast fan energy reductions of up to 60 percent versus heat pumps and air-handlers.<\/p>\n

\"UF_1\"<\/a>
Ogden Price – an HVAC technician at the University of Findleynear Toledo, Ohio – checks the operation of the school’s energy-efficiency mechanical system using an intuitive touchpad interface. <\/span><\/figcaption><\/figure>\n

A central outdoor air system (i.e.<\/em> DOAS) typically distributed small amounts of dehumidified outdoor air to the chilled beams to eliminate condensation on chilled beams, maintain comfortable room relative humidity levels and comply with ASHRAE 62, Outdoor <\/em>Air Ventilation Requirements\u2212Institutional Facilities<\/em>. In comparison with a typical heat pump or AHU forced air system, considerably less air is distributed to the chilled beams at significant lower fan energy costs.<\/p>\n

Geothermal HVAC systems are an ideal application for chilled beams. Utilization of higher-temperature chilled water (i.e.<\/em> 14 C [57 to 58 F]) allows for a greater capacity of cooling with less mechanical energy. Further, the geothermal borefield is not warmed as quickly because the amount of rejected energy is less per gallon of water cooled.<\/p>\n

Chilled beams improve the indoor environmental air quality through increased ventilation effectiveness, room quietness and good room air distribution. The geothermal side helps the exterior environment by reducing the amount of evaporative water consumed and carbon dioxide (CO2<\/sub>) emissions. The combination of the two building technologies makes it possible to achieve a low kBtu\/square foot energy consumption.<\/p>\n

Project specifics
\n<\/strong>For the Findlay project, the geothermal system supplies 14- to 17-C (58- to 62-F) closed-circuit ground-source water to ceiling-mounted, active chilled beams for handling 70 to\u202880 percent of the sensible load. Chilled beams reduce fan energy by up to 50 percent versus conventional air-handling technologies, so they comply and typically surpass the requirements of ASHRAE 90.1, Energy Standard for Buildings, Except Low-Rise Residential Buildings<\/em>.<\/p>\n

Each chilled beam requires only 2.8 to 3.5 m3<\/sup>\/minute (100 to 125 cfm) from the project\u2019s 538-m3<\/sup>\/minute (19,000-cfm) DOAS to prevent condensation. Additionally, chilled beams helped ASHRAE 90.1 compliance, because they reduced the required air-conditioning tonnage by approximately 25 percent versus a geothermal\/heat pump design.<\/p>\n

ASHRAE 62.1, Ventilation for Acceptable Indoor Air Quality<\/em>, defines requirements for ventilation, air-cleaning, design, installation, commissioning, operations, and maintenance. It specifies minimum ventilation rates and other measurements intended to provide indoor air quality (IAQ) acceptable to human occupancy and that minimize adverse health effects. DOAS can be integral to ASHRAE 62.1 in that they typically have high MERV filtration (i.e.<\/em> minimum efficiency reporting value) and specially sloped drain pans to minimize condensation accumulation that could potentially introduce mold to the supply airstream.<\/p>\n

\"UF_2\"<\/a>
The east side of the system, with the low-temperature chilled water pump supplying 7- to 8-C (44- to 46-F) water to the dedicated outside air system’s (DOAS’) chilled water coil in the foreground. <\/span><\/figcaption><\/figure>\n

The DOAS energy recovery is even more critical to surpassing ASHRAE 90.1 at the Davis Building. The 19 lab hoods exhaust considerably more air than similarly sized conventional buildings, thus greater amounts of conditioned outdoor air are required to maintain building pressurization.<\/p>\n

The building\u2019s embedded 12-mm (\u00bd-in.) diameter cross-linked polyethylene (PEX) floor tubing leverages the thermal mass of the three-story building\u2019s poured concrete. In this radiant system, piping under or inside the floor distributes the geothermal assembly\u2019s water. The temperatures cool or heat the slab, which in turn radiates to the spaces above and below.<\/p>\n

All combined, the chilled beams, radiant flooring, and DOAS provide even cooling and heating temperatures that are well within the six-degree Fahrenheit differential guidelines of ASHRAE 55, Thermal Environmental Conditions for Human Occupancy<\/em>. The three systems draw from the 107-m (350-ft) deep, 40-well borefield\u2019s three hydraulically separated geothermal earth heat exchangers using vertical loops of high-density polyethylene pipe (HDPE).<\/p>\n

\u201cWe see a tremendous opportunity with chilled beams and geothermal, especially north of the Mason-Dixon line where inherent ground temperatures of mid-50s (i.e.<\/em> 11 to 13 C) can be used in chilled beams and radiant systems,\u201d said Hamstra, a geothermal design engineer with more than 464,500 m2<\/sup> \u2028(5 million sf) of building space on his resum\u00e9. \u201cInstead of the 20 EER (i.e.<\/em> energy efficiency ratio) of a conventional chiller system operating a majority of the time, the University of Findlay system achieves an estimated 150 to 200 EER.\u201d<\/p>\n

The chiller, a 60-ton magnetic bearing model, runs about\u202820 percent less and is approximately four times smaller than\u2028a conventional chiller in a similar sized building, which helped reduce the project\u2019s equipment capital costs. The resulting 65 m2<\/sup> (700 sf)\/ton is unprecedented for a science-oriented building with 15 draft hoods that were 1.2 to 1.8 m (4 to 6 ft) in length, according to Hamstra, who has specified three chilled beam projects.<\/p>\n

\"UF_3\"<\/a>
The south end of the system, supplying the medium temperature 14- to 18-C (58- to 65-F) chilled water to the chilled beams and radiant floor. The closed-circuit cooling tower pump is seen in the background right. On the left side in the background, the shell and tube heat exchanger for a back up hot water supply from the existing boiler system is visible. However, this has virtually never been used other than during startup.<\/span><\/figcaption><\/figure>\n

The combination of a smaller chiller and no heat pumps, which are many times the more traditional geothermal choice over chilled beams, also complies and surpasses maximum pounds of refrigeration required by ASHRAE 15, Safety Code for Refrigeration <\/em>Systems<\/em>, and ASHRAE 34, Designation and Safety Classification of Refrigerants<\/em>.<\/p>\n

While these two standards are not new, the ever-changing scope of refrigerant types and quantities make the Davis Building environmentally cutting-edge for a facility its size. Additionally, both ASHRAE 15 and 34 are satisfied because Hamstra sized the building accurately and employed energy recovery (i.e.<\/em> DOAS) and chilled beam technology to reduce the facility\u2019s connected refrigeration load.<\/p>\n

Indoor air comfort
\n<\/strong>Hamstra specified 49 active chilled beams in 1.2-, 1.8-, and 2.4-m (4-, 6-, and 8-ft) lengths. As the ceiling-mounted chilled beams quietly cool air around their coils, the cooler air sinks while warmer air rises in a perpetual room air mixing scenario superior in air comfort and energy efficiency compared to fan coils, variable air volume (VAV), and other forced air methods.<\/p>\n

Installed by local mechanical contractor, Jack\u2019s Heating A\/C & Plumbing, the chilled beams have adjustable slots (nozzles) to address specific areas in its airflow range. The balance of air and water temperatures is all controlled by the building automation system (BAS). Hamstra also supplied each chilled beam room with a localized hot water reheat coil.<\/p>\n

\u201cWe reset the DOAS\u2019 discharge temperatures based on what most zones are calling for,\u201d he explained. \u201cThe localized reheat coils can provide a more precise temperature required in that particular zone.\u201d<\/p>\n

The outdoor air supplied through the active chilled beams also prevents potential floor condensation from the radiant system. Hot water for the chilled beams and radiant system is supplied via chiller condenser heat recovery. An adjacent campus building\u2019s conventional boiler serves as a backup, if needed.<\/p>\n

Perhaps the most differentiating factor from other geothermal designs is the project\u2019s intuitive Greensleeves\u2019 in-house software that optimizes efficiencies beyond traditional BAS parameters. \u2028By analyzing considerations such as set-point temperatures and historical data, and then interpreting space needs, the software provides several levels of predictive control based on the present and future temperature and humidity conditions of the building load, the loop and outdoor environment, while also managing the geothermal borefield. For example, the software might signal the chiller to increase the temperature of the radiant system\u2019s thermal mass on a morning where trends predict additional cooling will be needed in the afternoon.<\/p>\n

\"UF_5\"<\/a>
Factory-installed thermometer and digital temperature sensors on the system. <\/span><\/figcaption><\/figure>\n

The software also intuitively manages the borefield via the project\u2019s hybrid wet\/dry closed circuit cooling tower. The cooling tower can be used to pull heat out during cooler nights, without the expense of running the chiller, so the field can be more efficient the following day.<\/p>\n

\u201cThe software perpetually runs building load analytics and then reprograms itself every five days for better efficiency in a self-adapting approach,\u201d said Hamstra.<\/p>\n

Other alternatives to conventional HVAC systems that are controlled either with the Greensleeves\u2019 software or the BAS are:<\/p>\n