Godon Bloomquist: CASE STUDIES ______________________________________________________________________________________ ____________________________________________________________________________________________________________ 1 Under the auspice of: Division of Earth Sciences Chapter 2.9 Commercial and Industrial Heat Pump Case Studies R. Gordon Bloomquist, Ph.D. Senior Scientist Washington State University Figure 1. Geothermal Heat Pump System Schematic
Transcript
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
The Exchange is a three-story, semiocta-gonal commercial office building located inFarmington, Connecticut. The 265,000 squ-are foot complex, built in 1971, is an AIAaward winner. The building contains prima-rily office space, but a number of restaurantsand commercial establishments are found onthe ground and mezzanine levels. TheExchange was built as part of a Planned UnitDevelopment that also contains 500 single-family rental and condominium units.
The construction of The Exchange is ofexposed, heavy timbers without conventio-nal wall and ceiling finishes in both retailand office areas. The sloping roof with dor-mer-type windows keeps the building smalland low in scale for its size. The walls andceiling are insulated with 3.5 inches of mi-neral wood (R-13). The roof is asphalt shin-gle on _ inch plywood deck. The buildingcontains 7,500 square feet of insulated glass.Floors are a combination of concrete ongrade (1st floor) and heavy planks. Thebuilding has a recently-installed energy ma-nagement system (EMS). The $160,000 costfor the EMS had a one-year payback.
Geothermal Heat Pump SystemCharacteristics
Geothermal Source Description
The 55ºF geothermal source is providedby four wells that have been used
continually since 1971. The system uses ashell and tube heat exchanger between thewells and the circulating fluid that suppliesthe heat pumps. Well number 1, lying to theeast of the building, is 350 feet deep, andprovides 55 gpm. Wells 2, 3, and 4 lie to thewest of the building and provide 148 gpm,204 gpm, and 60 gpm, respectively. Thewells are all at a depth of 350 feet. Wells 1and 2 have 2-inch pipes to depth whilenumber 3 has a 3-inch pipe and number 4has a 4-inch pipe. Well number 1 is servedby a 7.5-hp pump, well number 2 by a 15-hppump, well number 3 by a 20-hp pump, andwell number 4 by a 10-hp pump. All of thepumps are submersibles. The water isdisposed of into a nearby creek at amaximum of ca 85ºF.
Heating, Ventilation, and Air-Conditioning (HVAC)
System Description
The system circulates tempered waterfrom the tube and shell heat exchanger toeach of the 495 individual water-to-air heatpumps that serve the building. The units aredesigned for a 20ºF _t in cooling mode and10ºF _t in heating mode. A 220-ton screwcompressor can provide supplemental heatto the loop in the winter, but since 1971,when it was installed, it has operated a totalof less than 8,760 hours or less than 3percent of the time. During the summer,when the loop temperature exceeds 100ºF, acooling tower rejects heat to the air. Thebuilding has a design heating loss of8,745,000 Btu/hour and a design coolingheat gain of 7,685,000 Btu/hour. Outside airventilation is 50,000 cfm.
The building is served by a total of 495individual heat pumps or a total of 1,094tons. The heat pumps range in size from 1 _tons to 4 tons. The 1 _ ton units have _ hpfans while the 2, 2 _, and 4 ton units all have_ hp fans. During periods of severe cold,the incoming well water can be boostedthrough the use of a Dunham Bush 220-tonscrew chiller run in reverse. During the
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
summer, the loop temperature can bemoderated by sending a portion of the waterto a cooling towers.
Selection of the Heat Pump System
The selection of the heat pump systemwas entirely consistent with the overallconcept of the project and the desire of theprincipals to make the complex asenvironmentally responsible as possible.The consulting engineers, James S. Mingesand Associates, Inc., also had previousexperience with the use of well water forcooling.
Operating History
The system has been in operation for 28years, and has been extremely reliable. Thebuilder/engineer, James Minges, calculatedin 1997 that the choice of the geothermalheating and cooling system had saved the“amazing amount of $5,200,000 in operationand maintenance costs over its first 27 yearsof existence over a conventional fossil fuelsystem.”
James Minges was honored for hisinstallation of the geothermal heating andcooling system in July of 1998 by theConnecticut Engineers in Private Practicewhen they presented him with the 1998Engineering Excellence ParticipationAward. The only major change that hasoccurred in the building heat pump systemsince the original design was the addition ofan energy management system in 1997.
It is interesting to note, however, thatthe building was designed, built, and inoperation prior to the oil embargoes of theearly 1970s, one of the prime driving factorsbehind the selection of geothermal heatpumps for many buildings selected after thattime. This building was indeed before itstime in not only design and construction, butalso the incorporation of the geothermalheating and cooling system.
Operation and Maintenance
Maintenance has never been a majorproblem throughout the system’s 28 years of
operation and operation. Most maintenanceis taken care of by in-house staff. Over 28years, only nine of the 495 units has had tobe totally replaced. Three of the down holepumps, however, have had to be replaced.The tube bundle in the shell and tube heatexchanger was replaced at a cost of $42,000.
In 1998, for example, nine compressorshad to be replaced. However, the work isdone in-house and total cost per unit is $700,including parts and labor. In addition, 11fan motors had to be replaced.
One major change in operation has beenthe requirement to install a monitoringsystem for environmental control of waterthat is dumped into a nearby stream. Themonitoring system cost $20,000, andsamples must be taken and sent in for testing4 times per year at a cost of $400 perquarter.
Total maintenance is estimated to beapproximately $0.16/sq.ft./year.
System Economics
James Minges, of The MingesAssociates, performed an energy analysis onthe building in 1997 and calculated that overthe 26-year operating history, the buildinghad saved approximately $5,200,000 ascompared to a conventional system made upof hot water boilers and conventionalchillers and cooling towers. He calculatedthat the 1997 maintenance cost was $0.16per square foot/year, operating costs amoun-ted to $0.60 per square foot/year, andreplacement costs $0.05 per square foot/yearfor a total of $0.81 per square foot per year.The total electrical load for the building in1997 was 4,552,560 kWh. This amounts to17.18 kWh per square foot/year. Based onthe numbers presented by Mr. Minges, theheat pump system uses ca 6.2 kWh persquare foot/year.
Satisfaction with the Geothermal HeatPump System
The present building owners andbuilding manager are extremely pleasedwith the system and stated in a July 8, 1998
International Course on GEOTHERMAL HEAT PUMPS______________________________________________________________________________________
news article in The Hartford Courat “Thedesign is really ahead of its time… has nevercomplained or heard of any other tenantcomplaints regarding the temperature.” The
director of maintenance also expresses totalsatisfaction with the system and its operationand ease of maintenance.
Haverhill Public Library
Location: Haverhill, MassachusettsBuilding Type: Public library, total 44,000
The Haverhill Public Library was builtin 1967. The original building was 27,000square feet; however, a 17,000 square footaddition was built in 1997, bringing the totalto 44,000 square feet. The building is ofconcrete construction and, in addition tocommunity library services, also contains anextensive historical volume section requiringprecise humidity control.
Geothermal Heat Pump SystemCharacteristics
Geothermal Source Description
The geothermal source consists of four1,500-foot deep standing column wells(SCW). Two of the wells are drilled toserve the initial retrofit of the building togeothermal heat pumps in 1994. Twoadditional SCWs were drilled in 1997 toserve the building addition. Average watertemperature is 55ºF. The water temperaturesin the SCWs varies from a summer high of69ºF to a winter low of 38ºF. Each of thewells may be pumped at from 70 to 80+gpm. Each of the wells was drilled sixinches in diameter; a four-inch pipe wasplaced in each well to depth. Pumping is viasubmersible pumps that draw from thebottom of the well. Discharge is to the topof the well between the standing columns
and the annulus of the bore hole. In order toensure relatively consistent water tempera-ture, a “bleed” system is coupled to the cir-culation loop and allows for ca 10 percent ofthe water to be bled off from the system,allowing for the reestablishment of the watertemperature if preset temperature parametersare exceeded. Each of the SCW submersiblepumps operates on a simple pressure logic.
Heating, Ventilation, and AirConditioning (HVAC)
System Description
The library was originally built with air-cooled chillers and electric resistance heat-ing. Conditioned air was distributed throughthree large air handler units. Control wasvia a pneumatic control system. The retrofitthat took place in 1994 included the drillingof two 1,500-foot deep standing columnwells and installation of six 10-ton water-to-water heat pumps. The electric resistanceelements were completely removed from theair handlers. The six heat pumps, located inthe original mechanical room, were tied intothe existing air handler system via a new andseparate building side manifold. The heatpumps are designed to supply up to 115ºFwater for heating and 45ºF for cooling.Building loop water temperature is manuallyset and automatically controlled by a singleaquastat. Each of the six heat pump stagesare sequentially called by set time delays.As each heat pump is called, an individualautomatic water valve at the heat pumpopens and pressurized well water flowsthrough the heat pump. The existingpneumatic control system was retained. Theheat pumps operate at a coefficient ofperformance (COP) of over 4.8.
In 1997, a 17,000 square foot addition tothe library was built and 13 water-to-air heatpumps were installed to heat and cool thisnew area. The 13 heat pumps represent 47.5
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
tons of new, installed capacity. Watersupply to these units is from two additional1,500 foot SCWs. The decision to usedistributed heat pumps instead of adding tothe central system was based on thecomplexity of providing additional servicebased on the existing air distribution systemand the need for more precise humiditycontrol in the new historical volume area ofthe library addition. Water from the twoSCWs is distributed to the heat pumps via apiping system served by two 3-hpcirculating pumps. The 13 distributed heatpumps are controlled by individualthermostats.
Selection of Geothermal Heat PumpSystem
The decision to retrofit the library in1994 after nearly 30 years of operation wasbased on a need to replace existingequipment and the availability of aMassachusetts Electric heat pumpdemonstration program that resulted in thesystem being installed at no cost to thelibrary. However, at the time of theaddition, no utility incentive program wasavailable and the decision was based on anevaluation of geothermal heat pumps vsnatural gas. The geothermal heat pumpswere chosen primarily as a result of a needto provide precise humidity control.
Operating History
Since being put into operation in 1994,the system has performed very well. Therehave, however, been some problems withcompressors with one unit failing almostimmediately and a second in 1998. The firstcompressor was replaced under warranty.The second unit resulted in an expenditureof approximately $2,000. The only otherconcern is the possible need to install a sandtrap or filter system to deal with sediment inthe system.
Operation and Maintenance
Maintenance is taken care of primarily byin-house staff and consists of routine
changing of filters and lubrication ofmechanical equipment, including pumps,fans, etc. No maintenance has been requiredon the standing column wells or submersiblepumps, but sediment in the system maynecessitate the installation of sand traps orfilters. Maintenance cost is ca $0.135sq.ft./yr.
System Economics
Due to the fact that Massachusetts Electricinstalled the first phase of the system at nocost to the library as a demonstration ofgeothermal heat pump technology, thesystem was fully instrumented with remotemonitoring data acquisition devices capableof collecting data every 15 minutes andincluding power usage monitor meters (kWhand kW) for both heat pumps and wellpumps. In the first full year of operation,the system saved a total of $11,586, showinga reduction in total electric bills of 23percent and a 65 percent reduction in costfor space conditioning. Of significantimportance to both the library and the utilitywas an approximately 50 percent reductionin demand. Unfortunately, similar data isnot available for phase two. However, for1998, the entire electric load for the librarywas 709,800 kWh for a total of 16.13 kWhper square foot per year. Maintenance isrunning approximately $0.135 per squarefoot per year.
Satisfaction with the Geothermal HeatPump System
Library administration and staff seem tobe very satisfied with the geothermal heatpump system. The decision to usegeothermal heat pump technology when theaddition was built in 1997 speaks well forthe satisfaction with the original system.Satisfaction with the system installed in theaddition appears to exceed that of phase one,and is probably due primarily to theindividual control and precise humiditycontrol that the system provides.
International Course on GEOTHERMAL HEAT PUMPS______________________________________________________________________________________
The headquarters building of the Churchof Jesus Christ of Latter-Day Saints (LDS)is a 28-story office tower plus penthouse andtwo 4-story wings to the east and west. Thebuilding was occupied in 1972. Construc-tion is concrete. The entire complex has683,000 net square feet of office space andhouses 1,600+ employees. Three levelsbelow ground contain the cafeteria, mailroom, print shop, maintenance shop, andparking for 1,400 cars. The GenealogyLibrary is on the main floor of the westwing. A 335-seat auditorium is on the mainfloor of the tower. The interior of the buil-ding is designed on 5-foot square modules.This permits separate control of lighting andair-conditioning for each module. On thebuilding’s exterior, T-shaped columns helpshade the windows to reduce the coolingload. The windows are double glazed, androtate so that external cleaning is notnecessary.
Geothermal Heat Pump SystemCharacteristics
Geothermal Source Description
The geothermal source is provided byfour wells. Two of the wells are ca 390 feetdeep, and the other two approximately 635feet deep. The two shallower wells areapproximately 67ºF and the two deeperwells are ca 75ºF. During normal winter
operation, water is pumped from the warmerwells and injected into the cooler wells.During the summer, the production andinjection are reversed. This results in agreater than normal _t between the wells andimproves operating efficiency. Well numberone is equipped with a 250-hp line shaftpump with the other three wells being fittedwith 200-hp line shaft pumps. Total flowduring any period of operation is 4,600 gpm.The facility has permission to produce up to6,285 gpm and inject up to 5,280 gpm.However, under normal operation,approximately 1,380 gpm is sent to thestorm drains and 3,220 gpm injected. Totalproduction capacity of the four wells is8,130 gpm.
Heating, Ventilation, and Air-Conditioning (HVAC)
System Design
The central heat pump plant consists ofthree 750-ton York units connected in series.Two heat pumps can cover peak load and, inmost instances, one heat pump will carry theentire building load. Each of the heat pumpsconsists of a turbo-compressor, condenser,cooler, and liquid intercooler, and ispowered by an 800-hp General Dynamicssquirrel-cage motor with geared-speedincreaser. The central system is controlledthrough the use of a Honeywell MasterControl Center. In utilizing the hot and coldwater produced in the refrigeration cycle,two main air heating and cooling systemsare used. The larger induction system isemployed around the periphery of thebuilding to balance heat loss and gainthrough the windows, while a dual duct,“high velocity” system is used in the interiorto balance the net occupancy and lightingload. In the induction system, both hot andcold water is delivered to separate primarycoils in a series arrangement in air streamswithin a common enclosure. These units,including 14 main air handlers, are locatedon the 13 th floor of the tower and the 4th
floor of the east and west wings.
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
In 1953, the church leadership expressedconcerns that existing city water service wasinadequate to provide necessary fire fightingcapabilities for the historic buildings onTemple Square. In 1954, the church beganto construct a 440,000-gallon, underground,concrete storage tank and two deep waterwells and pump stations to feed fire hydrantson Temple Square. In 1957, the cityproposed to meet their obligations for fireprotection by constructing an 8 inchdedicated underground fire line with firehydrants at strategic locations. In 1959, thechurch began to consider what should bedone with the storage tank. Consultingengineers proposed the feasibility of usingwater from wells number one and two forair-conditioning purposes. In 1960, thefeasibility study was started and submittalswere sent to the state for revised use of thewater. In 1962, the studies were completedand it was determined that two additionalwells were needed for injection. The statewater engineers gave approval and wellsnumber 3 was completed in 1963 and wellnumber 4 in 1964. In 1968, the constructionof the new church administration buildingwas started and it was completed in 1972.The system was also designed to provideprecool assist to the HVAC system of theRelief Society building.
Operating History
Since going into operation in 1972, thesystem has performed very well with fewmajor operational or maintenance problemsbeyond what would be anticipated during 27years of operation. According to the mainte-nance staff, the average life of the Yorkunits is 25 years, and that they have nowexceeded that and expect several additionalyears of life before major replacement isrequired.
Operation and Maintenance
Only one well has required extensivemaintenance. Well number one, completed
in May of 1955, has suffered two brokenshafts, the first in 1983 and the second in1995. The pump in well number one alsohas had bearings replaced in 1980 and 1994.Wells number two and three had sandseparators added in 1983, but no other majorchanges or repairs have been required. Thepump in well number 4 had to be pulled in1981 to replace the head shaft because ofleaking seals. In 1995, the entire pump inwell 4 was pulled to install new bearings.Both wells number one and four have hadthe well brushed and cleaned.
All three of the heat pumps have had tobe retubed. Chiller number 1 in 1988,chiller number 2 in 1990, and chiller number3 in 1987. The average cost of retubing hasbeen $80,000 to $100,000. The compressoron unit number 3 was rebuilt in 1987, andthe compressor on unit number 2 was rebuiltin 1990. The cost of rebuilding a compres-sor is ca $15,000. Total maintenance cost isestimated to be $0.13 to $0.15 sq.ft./year.
System Economics
The system has always been extremelycost effective for the church. It was calcu-lated that the system had a four yearpayback although it had cost one-third morethan a more conventional system based onboilers and chiller with cooling tower.However, it should be remembered that twoof the wells were drilled for other purposesand are not included in the first cost of thesystem. In 1982, the electrical cost for thebuilding was estimated to be 0.03¢ persquare foot, of which an estimated 50percent was for lighting and the remainderfor mechanical equipment.
Satisfaction with the Geothermal HeatPump System
Church personnel seem to be extremelypleased with the overall operation andmaintenance requirements. In fact, the headof maintenance said, “great system, wouldrecommend again.”
International Course on GEOTHERMAL HEAT PUMPS______________________________________________________________________________________
condominium complexSystem Type: Open loop, central and
water source heat pumpsystem
Age: 34 yearsEnergy Use: 15.35 kWh/sq.ft./year –
Total 8.43 kWh/sq.ft./yrfor the mechanical system
Estimated Maintenance Cost: approxi-mately $0.12 to $0.15/sq.ft./yr.
Building Characteristics
The Parkview Apartments in Manches-ter, Massachusetts, was opened in 1965.The 207, 400-square foot complex is built asa perfect semi-circle and frames a two-acrelandscaped courtyard. Each of the apart-ments opens onto a balcony overlooking thelandscaped courtyard, including rock gar-dens bordering on a succession of ponds,bridged streams, and miniature waterfalls.The 8-floor structure and full basementcontains 318 units, including studios andone- or two-bedroom units. The back wallof the complex encloses hallways andshelters the apartments from wind andreduces energy losses. The exterior is ofprecast concrete panels with 1 inch ofurethane insulation (R-7). The roof is built-up tar and gravel on 2-inch urethaneinsulation (R-14) over 8-inch precastconcrete deck. The gross wall area is 80,250square feet with glass covering 39,120square feet. The design heat loss is5,200,000 Btuh with a ventilation require-ment of 19,200 cfm. The design heat gain is3,600,000 Btuh with a ventilation requi-rement of 19,200 cfm.
In April of 1980, the Parkview Apart-ments was converted to a condominium, andhas been operated as a condominium com-plex since that time.
Geothermal Heat Pump SystemCharacteristics
Geothermal Source Description
The complex was originally served bythree wells; however, the system now relieson two wells. The depth is estimated to beca 80 feet. The two wells provide approxi-mately 1,500 gpm of ca 54ºF water.Pumping is via 30-hp, 78-foot vertical shaftpumps. Operation of the system requires theuse of only one well with the second inreserve except during peak demand periods.An Alpha Laval plate and frame heatexchanger separates the well water from thein-building circulation system. Water, afterpassing through the heat exchanger, feedsthe ponds that cascade through the courtyardand finally drains into a nearby stream.
Heating, Ventilation, and Air-conditioning (HVAC)
The original system consisted of three200-ton Chrysler Air Temp water-to-waterheat pumps. Each of the three units isequipped with two 100-ton compressors.The heat pumps operate at a COP ofbetween three and four. Water heated orcooled by the heat pump is circulatedthroughout the complex via two 75-hpcirculating pumps supplying a two-pipesystem allowing for the supply of eitherheating or cooling. The system circulates upto 2,000 gpm. During the winter, water issupplied to the individual fan coil units atfrom 95º to 110ºF. During the summer,52ºF water is circulated to the fan coils fromthe central heat pumps. During the shoulderperiod, the system circulates 59ºF water thatcan be produced by rejecting heat directly tothe well water via the plate and frame heatexchanger. The system also includes a3,000-gallon hot water accumulator and a1,000-gallon chilled water accumulator.Water circulates to each apartment where itsupplies a total of 950+ fan coil units.Temperature in the individual units is regu-lated by means of wall-mounted pneumaticheating/cooling thermostats and modulating
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
valves in the fan coil units. For domestichot water, incoming city water passesthrough a tube nest within the heataccumulator and then passes to a storagetank where it mixes with water from thebooster heater to bring it up to desired taptemperature.
Selection of the Geothermal Heat PumpSystem
The apartment complex was built uponthe site of a former tannery that had requiredvery large volumes of water. The availa-bility of water provided the developer withthe possibility of using water-to-water heatpumps. The structural aspects of the buil-ding design precluded consideration oflocalized through-the-wall cooling equip-ment and mandated that a central spaceconditioning system would have to beadopted. The decision thus became one ofeconomics and the first-cost differentialbetween the costs of an oil-fired boiler plantwith its housing, stack, fuel storage facilitiesand chillers and cooling tower, etc., and thecost of the heat pump system. Thedifferential turned out to be small. The finalselection would therefore be based onoperating cost and, after extensive analyses,it was determined that the heat pump systemwould have substantially lower operationand maintenance cost.
Operating History
The system is now over 30 years old andis definitely showing its age. One of theChrysler Air Temp heat pumps failedseveral years ago and, because replacementparts are no long available, had to be takenout of operation. The other two units conti-nue to operate, although the condominiumassociation is now looking at other heatpumps to replace those that are now in use.Several years ago, the association installedthe Alpha Laval plate and frame heatexchanger and they are very pleased with itsperformance. The two-pipe system doesrequire a certain amount of crystal balling asthe system has to be changed manually fromheating to cooling mode and vise versa.
Once the change is made in the fall andspring, they are reluctant to change back.This can result in some days where air-conditioning would be desirable but theyfeel it is better to error on the side of beingable to provide heating. This does notappear to have been a major source of com-plaint, but it appears that a four-pipe systemwould be the preference if retrofitting thecomplex were feasible.
Operation and Maintenance
The system has operated very success-sfully for over 30 years, and has served thetenants well. At this point, maintenance is,however, becoming a problem and systemreliability is coming more and more intoquestion. At this point, maintenance andrepair is running as high as $80,000 peryear; however, the expected range is ca$25,000 to $30,000. The wells and especi-ally the pumps appear to be requiring muchmore maintenance than would normally berequired. They have to pull the pumps everyother year. One potential cause for this isthat the pumps are not fitted with variable-speed drives, and it appears that a conside-rable amount of sand is drawn into thesystem, most likely when the pumps arestarted. Normal operation is taken care ofby the condominium association, andmaintenance is also coordinated by one ofthe association board members who has avery good understanding of the system andits maintenance and operational require-ments.
System Economics
When the system was first built (1965),the owner, Edward Brendt, calculated thatheating and cooling was costing an averageof only $6.10 per apartment per month, orapproximately $0.11 per square foot peryear. At this time (1998), heating andcooling requires 8.43 kWh/square foot/year,while total electrical consumption is 15.35kWh/square foot/year (1997). Maintenancecosts are calculated to run approximately$0.12 to $0.15/square foot/year. Thecondominium association is, however, ex-
International Course on GEOTHERMAL HEAT PUMPS______________________________________________________________________________________
pecting to incur a major expense in the nearfuture as the heat pumps are definitely at apoint where they need to be replaced toensure reliability. Continued tracking of thisfacility through the change out and over thenext several years of operation would appearto provide an excellent opportunity.
Satisfaction with the Geothermal HeatPump System
There seems to have been a high level ofsatisfaction with the system over the years,
and only recently has the system deterio-rated to the point where maintenance andrepair costs are rising and major replacementdeemed to be a necessity. The one singleitem that would appear to be a source ofdissatisfaction is the two-pipe system allow-ing for only the supply of either hot orchilled water but not both. This appears tobe an almost universal problem, and two-pipe systems should be avoided in favor offour-pipe system whenever possible.
Benton PUD
Location: Kennewick,Washington
Key Contact: Nancy Philipp, EnergyAdvisor
Geothermal Source:Ground source,horizontal loop
System Type: closed loop,water-to-air heat pumps
Age of System: 3 yearsBuilding Type: 31,000 ft2office
buildingEnergy Use: 18 kWh/ft2
System Designer: SCM Engineering
Building Characteristics
The new headquarters for Benton PUD wasoccupied in January 1994. The buildingprimarily consists of office space, but alsoincludes a customer service area and anauditorium that is regularly used for publicmeetings and events. Construction is stickframe with a masonry facade. This is anenergy-efficient-building featuring efficientlighting, occupancy sensors, an efficientbuilding envelope, and variable speed driveson pumps.
Geothermal Heat Pump SystemCharacteristics
Ground Source Description:
There is a horizontal ground loop underthe parking lot and grass area east of thebuilding. There are three sets of loops in
three layers for a total of nine overall loopsthat feed into a header in the mechanicalroom. Within each set of loops there areseven to eight individual loops. The firstlayer of pipes was put in six inches of sandcovered by three feet of fill followed by thesecond layer of pipes in six inches of sandcovered by three feet of fill, then the thirdlayer of pipes in six inches of sand andtopped off by six feet of fill. The loopscover an area that is approximately 160 feetby 166 feet. There are two 5-hp pumps thatpump a potassium acetate (GS-4) heattransfer solution through the ground sourceloop. The pumps are equipped with variablespeed drives. Only one pump operates at atime.
Heating, Ventilating and AirConditioning (HVAC) System
Description:
The HVAC system consists of ninewater-to-air heat pumps for spaceconditioning and one water-to-water heatpump for domestic hot water. The heatpumps use the ground source potassiumacetate loop as a heat source when heatingand a heat sink when cooling. There arevalves at each heat pump to allow theground loop to bypass the heat pump when itis not heating or cooling. The total designheat pump capacity is 77 tons.
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
Each heat pump serves a zone in thebuilding. They are constant volume units.They have 2-stage compressors with econo-mizers. A thermostat in each room controlsa damper to allow some individual roomcontrol within each zone.
Selection of the Geothermal Heat PumpSystem
The PUD wanted an attractive buildingthat showcased energy efficiency for thecommunity. An energy study wasperformed that compared air-to-air heatpumps and the geothermal heat pumps to abaseline system with electric resistanceheating and DX cooling. The payback forthe geothermal heat pump system wasrelatively long, even with a $44,700 rebatefrom the Bonneville Power Administration(22 year payback). However, thegeothermal heat pump system was clearlythe most efficient, using less than half theenergy of the other options. They alsoexpected it to have lower maintenance thanan air-to-air heat pump system which isexposed to greater temperature extremes.
The commissioners were favorablydisposed toward a geothermal system. Onecommissioner had a water source heat pumpsystem for his residence and others werefamiliar with residential systems. They alsovisited several other non-residentialbuildings with similar geothermal heatpumps.
Operating History
The PUD has had some difficultyachieving stable operation from thegeothermal heat pump system. When theyfirst occupied the building in January 1994,the ground loop temperatures got down to18°F. They were concerned about thepotassium acetate freezing solid in the loopas this temperature was very close to its lowend temperature range. To reduce the loadon the ground loop and to prevent the loopfrom freezing they used electric spaceheaters to aid in heating the building. Thefirst summer the loop temperature leavingthe building reached 126°F and the return
was 119°F. The heat pump units weretripping off because of high head pressure.They could not bring the heat pumps backon until the head pressure dropped. Sincethe first year there has been someimprovement as the ground loop has “settledin.” Now in the winter the loop temperaturegets down to the low 40’s and last summer itgot up to the high 90’s. They hope thisimprovement continues.
They have been told since theinstallation that it can take up to five yearsfor a ground loop to “settle in.” The processof settling in involves the elimination of airpockets in the soil and the rehydration of thesoil which dried out during the constructionprocess. This process improves heat transferbetween the ground loop and the soil. They believe some of the problemsmaintaining and controlling the ground looptemperature are related to a lack of moisturein the ground. Moisture in the ground isimportant for heat transfer. They have claylike soil that looses moisture rapidly.Having some kind of leach line that wouldallow them to introduce water and controlthe moisture content in the soil wouldimprove heat transfer.
The original design strategy was tooversize the loop capacity. They weresupposed to need only seven of the nineloops so that there would be extra capacityfor additions to the building. However,because the ground loop temperatures havebeen worse than expected, they have beenusing all nine loops. The factors affectingheat transfer with the soil noted aboveeffectively reduce the heat transfer capacityof the loop. Another contributing factorcould be the three-layer ground loop design.The three ground loops are stackedrelatively close together which would tendto reduce the capacity of the ground loop.
They are also trying to reduce systemrun time by shutting the system off at 6 p.m.Extended hours of operation don’t allow theground loop to recover, reducing thecapacity of the system. Some of theproblems when the building was firstoccupied may have been due to a bake outof the building to remove volatile chemicals.
International Course on GEOTHERMAL HEAT PUMPS______________________________________________________________________________________
Heating the building to 90°F for the bakeout took a lot of heat out of the ground and itdid not recover before occupancy. Anotherstrategy they have used during the hottestpart of the summer is to heat the building atnight and on weekends to help cool theground loop. They remove any excess heatin the building using the ventilation systemin the cool of the morning.
They have had some problems withtemperature control across the zones in thebuilding. Some zones include perimeterareas with different orientations as well asinterior areas. They plan on splitting someof these zones by adding another heat pumpand converting the domestic hot water heatpump to a space conditioning unit for someof the core spaces.
There are also some control problems.One of the most baffling occurs onlyoccasionally when the system is in airconditioning mode. As the need for coolingincreases, the central direct digital controlsystem calls for 2nd-stage cooling. The heatpump has not been responding to the controlsignal. They manually have to trick the heatpump into going to 2nd-stage cooling bycreating an emergency situation. Thechallenge in solving this problem is that onevendor claims it is a central control systemproblem and the other vendor claims it is aproblem with the heat pump controls.
Operation and Maintenance Issues
On the heat pump side, the maintenanceis no different than what you would expectfor a typical system. They have a preventivemaintenance program that includes changingthe filters, checking the belts, inspections,etc. Two compressors have failed on one ofthe heat pumps. Both were replaced underwarranty. The biggest maintenance headache hasto do with the potassium acetate heattransfer fluid that is in the geothermal loop.They selected this heat transfer fluid becauseit is very environmentally benign. It is nothazardous and does not require any specialhandling if it spills or leaks. However, therehave been extensive problems with leaking.
The original installation used teflon tape onthe fittings in the geothermal loop. Forpotassium acetate, plumbers putty needs tobe used. When the system goes from winterto summer operation and the heat transferfluid expands, there are lots of leaks. Thismakes a mess. They have had leaks in theceiling in a number of places in the building.The leaks are very disruptive and are noteasy to repair. Even though the potassiumacetate is environmentally benign, it has anacidic smell and feel and really isn’t thatpleasant. It is also corrosive when exposedto air. Some of the plumbing fittings on thesystem look they are 20 years old. Theirblack moly fittings are not lasting. Theyalso believe that the failure of all the bypassvalves to the heat pumps is due to this heattransfer fluid. Because the valves to the heat pumpshave failed, the heat transfer fluidcontinually flows through each heat pump.As a result, the pumps on the ground loopalways run at full load and have not beenable to take advantage of their variablespeed capability. Both motors on the ground loop pumpshave been reconditioned and they replacedboth shafts. It is not clear what the problemis, but they believe it may be due to negativepressure on the pump due to leaks. Therewas a lot of cavitation damage on the shaftsand pumps and the unstable load may bestressing the motors.
System Economics
An energy study was completed prior tothe design of the Benton PUD HeadquartersBuilding. The study compared a geothermalheat pump system and air-to-air heat pumpsystem to a baseline electric resistance heatand direct expansion cooling system. Table1 summarizes the results relative to thebaseline.
The Bonneville Power Administrationprovided a $44,700 rebate for thegeothermal heat pump system, whichreduced the payback to 22 years. A packageof efficiency measures including increasedwall and roof insulation, high efficiency
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
windows, reduced glazing area, highefficiency lighting, and occupancy sensorswas installed. A rebate of $62,850 wasprovided for all these measures, which wereestimated to reduce energy consumption by
39 percent (229,320 kWh/yr). The simplepayback of all the efficiency measureswithout the rebate was 13.8 years. Therebate reduced the payback for the utility to4.7 years.
Table 1.Comparison of HVAC System Incremental Costs and Savings
IncrementalCost ($)
IncrementalEnergySavings
(kWh/yr)
IncrementalEnergy
Savings (%)
IncrementalEnergy Cost
Savings($/yr)
SimplePayback
(yrs.)
Air-to-Air HeatPump
12,345 35,991 6.1 1.080 11.4
GeothermalHeat Pump
124,560 122,011 20.8 3,660 34.0
Clearly, the selection of the geothermalheat pump system was not based purely oneconomics. When the interactive effects ofthe other measures are considered, the actualpayback would be longer than 22 years. Thegeothermal heat pump is clearly the mostenergy-efficient choice and the desire of theutility to demonstrate this technology wasthe overriding factor in its selection.
Actual energy use in the building hasbeen greater than estimated in the energystudy. For the year ending in March 1997,building energy use was 559,920 kWh (18kWh/sq.ft.-yr). This is 56 percent higherthan the energy study estimate. The PUDhas a meter on the building HVACequipment. Energy use by the HVACequipment was 236,930 kWh for the yearending on March 1997. This compares to34,724 kWh estimated in the energy model.This dramatic of a difference draws intoquestion the validity of the energy model. Itappears the model significantly underesti-mated fan and pump energy. The geo-thermal system is also operating less effici-ently than expected due to the extremeground loop temperatures, longer hours ofoperation to maintain temperatures, pumpsnot unloading due to failed valves, and othercontrol problems. These results suggest thegeothermal heat pump system is not meetingperformance expectations and is saving very
little, if any, energy. However, as theground loop continues to settle in and the
problems with the failed valves are addres-sed, the geothermal heat pump system willbegin to produce savings.
Satisfaction with the Geothermal HeatPump System
Benton PUD was not satisfied with theinitial performance of their geothermal heatpump system. If the first year problemswould have continued, they would have hadto find a solution like adding a cooling toweror boiler. Fortunately, some of the problemsseem to be correcting themselves as theymake adjustments and the system settles in.They still have the issue of the potassiumacetate and whether to keep dealing with theleaks or go to the expense of replacing it. One of their concerns is the amount oftime and money they have put into this newsystem to deal with a number of operationand maintenance problems. The averagebuilding owner might not have access to theresources the PUD has to deal with thesemaintenance problems. The PUD expectedmany years of trouble free operation afterthe initial shakedown period. They still believe in the geothermal heatpump concept. They realize most of theproblems they are experiencing are due to
International Course on GEOTHERMAL HEAT PUMPS______________________________________________________________________________________
Geothermal Source: GroundwaterSystem Type: Open loop, two 150-
ton water to waterheat pump
Age of System: 14 yearsBuilding Type: 180,000 ft2 County
Correctional Facility,including courtrooms, and inmatequarters and supportfacilities.
Energy Usage: 20.69 kwh/ft2/year$0.917/ft2/year
Building CharacteristicsYakima County Correctional Facility
The main building containing court rooms,jury rooms, inmate quarters, and supportfacilities was completed in 1983, and is afour-story, concrete block structure. A60,000 ft2 annex of similar construction wasadded in 1991.
Geothermal Heat Pump SystemCharacteristics
Groundwater Source Description
The facility is served by one 900 footdeep, 8 inch diameter well capable ofproducing 600 gallons per minute of 70+°Fwater. The 30-horsepower pump is drivenvia a variable speed drive, and is set at 260feet. The water is pumped to two plate andframe heat exchanger where a delta T of sixto eight degrees is removed. Thegeothermal water is then pumped to aninjection well where the water is returnedback to the producing aquifer.
Heating, Ventilation, and AirConditioning (HVAC) System Description
The mechanical room contains two plate andframe heat exchangers, two 150-ton Traneheat pump and a 600 kW, 1,588 amp, 4,620
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
MBtuh electric boiler. In addition, thesystem uses a cooling tower for heatrejection. A four-pipe system circulates theheated or cooled water to air handlers thatare located throughout the building. Two15-horsepower pumps circulate water forheating and two 10-horsepower pumps areused for circulating chilled water.
Selection Criteria
Selection of the Geothermal Heat PumpSystem
At the time the Yakima CountyCorrectional Facility was being planned, thecountry had just experienced the secondmajor oil crisis in a decade, and oil andnatural gas prices were escalating rapidly.The Yakima County Commissioners wereintent on finding the most cost-effective,energy-efficient, and secure energy alternatefor the planned 265-bed correctional facility.
Technical studies were provided to theCounty by the Washington State EnergyOffice, the Oregon Institute of TechnologyGeo-Heat Center, and Pacific Power. Thesestudies evaluated the opportunity for and therisk of obtaining adequate supplies ofgeothermal fluids, the technical feasibility ofusing heat pumps to meet the heating andcooling needs of the proposed facility, andthe economics of the heat pump optionrelative to the use of natural gas and/orelectricity. These studies plus the existenceof a 85°F flowing artesian geothermal welldrilled in the early 1900s, only a few blocksfrom the planned construction site, andinformation concerning the economicalfeasibility of installing a geothermal heatpump system were all the Commissionersneeded to choose the heat pump system overother alternatives.
Operating History
The Yakima County correctional facilitywas commissioned in 1983. Within weeksof commissioning, the geothermal heatpump system began experiencing extremelyhigh and totally unacceptable levels offcorrosion. The system had to be shut down
and the County contacted the WashingtonState Energy Office (WSEO) and requestedhelp in determining causes of the problemsand measures that could be taken tominimize or eliminate these problems.WSEO, in turn, brought in the OregonInstitute of Technology Geo-Heat Center(OIT) to undertake the engineering studies.Although the water had been tested prior toselecting the heat pump system and found tobe potable, a number of poor engineeringdecisions led to the problem encountered.The primary causes of the corrosion werethe use of an open to the atmosphere holdingtank, and a decision to circulate thegeothermal water directly throughout thebuilding, i.e., no heat exchangers were usedto separate the geothermal fluids from thepiping and air handlers found throughout thefacility. Another major problem involvedthe use of a fixed speed pump. Theproduction well pump which, upon start up,caused considerable turbulence in the welland resulted in large amounts of sand beingintroduced into the system.
OIT engineers recommended severaldesign and operational changes to thesystem. First was to eliminate the openholding tank that was allowing oxygen toenter the system, and second was to isolatethe geothermal fluid loop from theinbuilding distribution loop. This was donethrough the addition of plate and frame heatexchangers. The third major design changewas to add a variable speed controller to theproduction pump that would minimizeturbulence at start up and eliminate theproblem of brining sand up from theproduction zone. These changes completelyeliminated the operational and corrosionproblems that had been encountered but at asignificant cost to the County. These costsincluded engineering, purchasing newequipment, construction, and possibly mostsignificant, the County was forced to use anelectric boiler throughout the reconstructionperiod. Unfortunately, these costs resultedin lengthy legal proceedings with the Countyfinally prevailing.
International Course on GEOTHERMAL HEAT PUMPS______________________________________________________________________________________
The system has operated verysatisfactorily from a mechanical standpoint,with the only major problem being onecompressor that has been rebuilt on anumber of occasions. The other three com-pressors have required little maintenance.
The system has, however, experiencedtwo problems with the geothermal supplyand disposal system. The Yakima area hasexperienced a significant lowering of thegroundwater table over the past severalyears due to several years of draughtconditions and increased groundwater usage.The lowering of the static water level in theproduction well required that the productionpump be reset and nine sections of pipeadded. The system has also experiencedsome problems with the injection well beingable to accept no more than 250 gpm ofspent geothermal fluid without increasingpump pressure. The exact cause of theinjection problem has not been determined.If the situation worsens, the County will beforced to increase pumping pressure, workover the existing injection well, or drill asecond injection well.
Satisfaction With the Geothermal HeatPump System
The County has been very satisfied withthe system despite the initial problem thatresulted in lengthy legal proceedings. Thesystem has proven to be very easy tomaintain, and has met the demands of theincreased load without major systemexpansion or modification.
Problems that have been related to oneof the four heat pump compressors is not inanyway directly related to the geothermalsystem.
Problems with the declining acquifer,the requirement to reset the productionpump, and what appears to be an increasingproblem of pressure building up in theinjection well have been and continue to beof major concern. The County may beforced to work on the injection well or drilla second injection well.
If acquifer draw down or injectionproblems worsen, operation and mainte-nance personnel have indicated that theymay be forced to look at alternative opera-tional strategies and/or system options. Todate, however, the system has continued toprovide reliable service is a cost-effectivemanner, and county officials have experi-enced strong support for and confidence inthe system.
Beaver Lake Middle School
Location: Issaquah,Washington
System Type: Closed Loop, WaterSource Heat PumpSystem
Age of System: 3 yearsBuilding Type: 109,000 ft2 middle
schoolEstimated Energy Use:11 kWh/ft2
Estimated Maintenance Cost: n/aSystem Designer: Tres West
Engineers, Inc.
Building Characteristics
Beaver Lake Middle School was occu-pied beginning with fall classes in 1994
(note that during design the school wascalled Plateau Middle School). The buildingis a two-story 109,000 square foot structureserving 570 students. A track and grasssports field is located to the southeast of the
building. The building layout is a crossshape and includes music rooms, stage andcommons area, library, main gymnasium,and auxiliary gym. Two-story classroomwings extend out each side with shop areasand a kitchen included in the west wing.Administrative offices are located at thejunction of the east wing.
Construction is primarily CMU withmetal stud framing and metal deck roofingwith asphalt shingles. The floors are con-crete and glazing is double-pane with
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
thermal break in aluminum frames. There isa large quantity of skylights over the gyms,library, and commons area. The buildinghas an energy-efficient envelope, efficientlighting system with occupancy sensors,energy management system with digitalcontrols, and variable speed drives onpumps.
Geothermal Heat Pump SystemCharacteristics
Ground Source Description:
The ground-coupled water source heatpumps utilize a horizontal ground loop heatexchanger for a heat sink in lieu of a coolingtower and supplemental boiler. Thehorizontal loop consist of 162,500 linear feet(650 ft. per ton) of 1” diameter polybutylenepiping in two layers (4 ft. and 6 ft. deep)spaced 2 feet apart. The piping is buriedbelow the football and baseball fieldssoutheast of the building. There are three (3)circulation pumps equipped with variablespeed drives.
Heating, Ventilating and AirConditioning (HVAC) System
Description:
The system consists of 52 Water SourceHeat Pumps located in ceiling spaces. Eachheat pump serves a zone in the building,either one room or a portion of a largerroom. The total design heat pump capacityis 250 tons. An 840 kW electric boilerprovides auxiliary backup heating.
The system is constant volume with athermostat controlling each zone. Systemcontrols modulate the pumps as required tomeet the loads. Piping and valves at eachheat pump provide bypass flexibility formaintenance and repair. The heat pumpwater loop is sized to provide requirementsfor the whole building (520 gallons perminute) if all heat pumps were workingsimultaneously.
Selection Criteria
Issaquah School District wanted amodern, efficient middle school that wouldprovide a great learning environment. TheDistrict has had success with water sourceheat pumps and had a larger site whereground coupling could be implemented. Anenergy study was provided by Puget SoundPower and Light.
The geothermal system was clearly themost efficient showing $33,622 in yearlyenergy savings relative to the baselinesystem. Financial incentives provided byPuget Sound Power and Light covered theincremental costs of the geothermal systemand convinced the District to try the newtechnology.
Operating History
Issaquah School District has haddifficulty achieving stable operations fromthe geothermal heat pump system. Duringthe first year of occupancy they began toexperience leaks throughout the system.These leaks occurred at all of the valves andconnections at the heat pumps. Therecommended solution was to replace thenon-toxic gylcol refrigerant with water.
Many adjustments were required in theoperations because of the change. Thereplacement of the refrigerant created manyair pockets in the lines which caused thelack of proper flow to the heat pumps. Thisresulted in the units tripping off because ofhigh head pressure. The second year ofoperation required a lot of maintenance staffhours to adjust the operation to use water asthe heat transfer fluid and removing airpockets.
The system now seems to be operatingproperly with loop temperatures beingmaintained at 50°F. The electric boilerautomatically comes on when temperaturesfrom the ground loop drop below 50°F. Thesystem is sufficiently able to maintaincomfortable conditions in all zonesaccording to maintenance staff.
Operation and Maintenance Issues
International Course on GEOTHERMAL HEAT PUMPS______________________________________________________________________________________
General maintenance for the system hasbeen no different than expected for a typicalheat pump system. The biggest maintenanceproblems have been caused by the glycolheat transfer fluid in the geothermal loop.
The system leaked due to brass fittingcorrosion during the first year. Many differ-ent Teflon tapes were tried unsuccessfully tostop the leaking. The leaks persisted duringthe first year necessitating the replacementof many ceiling tiles. Some valves havebeen replaced but the corrosion is stillevident throughout the system.
The glycol fluid was removed and thesystem was cleaned and replaced with waterthe second year. Unfortunately air wastrapped in lines causing problems the secondyear. Air vacuum causes an interruption inthe flow of water and the heat pumps shutoff due to high head pressure. The heatpumps then are taken out of service usingthe bypass valves and maintenance isperformed to remove air from the lines.
Adjustments also had to be made by trialand error to modify flows and temperaturesbecause of the different heat transfer fluidcharacteristics. The system now appears tobe working with routine maintenance requi-rements. There are still concerns about futu-re maintenance requirements such as dama-ged valve and fitting replacement.
System Economics
An Energy Smart Design AssistanceReport was completed prior to the design ofBeaver Lake Middle School. The study con-sidered several system options. The baselinesystem was water source heat pumps withelectric boilers and constant speed pumps.Options included variable pumping, watersource heat pumps with gas boilers, and thegeothermal heat pump system. Table 1summarizes the results relative to thebaseline.
Table 1. Summary of HVAC Analysis
SYSTEM SYSTEMCOST($)
ENERGYUSE(kBtu/YR)
ENERGYCOSTS($)
ENERGYSAVINGS($)
SIMPLEPAYBACK (YRS)
WSHP- Elec BoilerConst Spd Pumps
BASELINE$1,015,303
6,933,197 $93,322 BASELINE
WSHP-Elec BoilerVFD Pumps
+ $27,230 6,542,555 $88,065 $5,257 5.18
WSHP- Gas BoilerConst Spd Pumps
- $ 7,450 7,620,264 $92,530 $ 792
WSHP- Gas BoilerVFD Pumps
+ $19,780 7,229,622 $87,293 $7,584 2.61
WSHP-Grnd SourceElec Boiler
+ $84,563 4,686,927 $65,802 $27,520 3.07
WSHP-Grnd SourceElec Boiler- VFD
+ $112,908 4,252,159 $59,700 $33,622 3.36
Puget Sound Power and Light provideda $112,908 rebate for the geothermal heatpump system, which reduced the payback to0 years. The system was estimated toreduce energy consumption and save BeaverLake School District $33,622 yearly. The
simple payback without the rebate wouldhave been 3.36 years.
The selection of the geothermal heatpump system was based primarily on theeconomics and the desire of the District tobuild a modern efficient facility for itsstudents and staff.
Godon Bloomquist: CASE STUDIES______________________________________________________________________________________
The District has no comparable schoolfacilities and therefore is not aware ofwhether this school is saving money relativeto similar schools. The actual energy cost in1996 was $15,000 greater than the estimatefrom the Energy Smart Design Report.However, this was mostly due to an increasein electric rates. Actual energy use for thefacility was 4,179,099 kBtu, several percentless than the study estimate. Adjustingoriginal baseline energy costs for the currentelectric rates results in an annual baselineenergy cost of $121,884. Relative to thisnew baseline, the District is saving over$45,000 annually, which is more than theoriginal savings estimate.
Satisfaction with System
Issaquah School District is not satisfiedwith the geothermal heat pump system. Thefirst year they spent a lot of time dealingwith leaks and the second year adjusting the
system to use water as the heat transferliquid. They also had to contend with manydisruptions due to air trapped in the lines asa result of the switch in heat transfer fluids.Although the maintenance problems nowseem minimal, there are still concerns aboutthe possible long-term maintenance cost ofreplacing valves and fittings corroded by theglycol heat transfer fluid.
Because of the problems they have had,the District believes the system has notrealized the energy savings they werepromised. They also believe newtechnologies should not be tested in publicschools where resources are not available tohandle operation and maintenance problems.
They still believe the geothermalconcept is sound, but have no faith in theability of engineering to deliver thetechnology. They believe the engineer musthave more knowledge and experience beforethe system can be installed successfully.
