GeoExchange Design Integration. Steven Carlson, P.E. CDH Energy Corp

Transcription

1 GeoExchange Design Integration Steven Carlson, P.E. CDH Energy Corp

2 What is it? Couples the building to the environment Exchanges heat: to the ground for cooling from the ground for heating Efficiency is its first attraction Simplicity in operation and maintenance Commercial applications growing Decades of history (600+ schools)

3 New York Hotel Iowa Courthouse Wisconsin High Schools Evansville Fond du Lac Michigan Restaurant Pennsylvania Office

4 What is it? Rather than central chillers and boilers, system uses smaller unitary heat pumps ¾ to 5 tons in each space central loop pump ground coupling Ground coupling methods defined system type open loop / closed loop vertical bores pond / other

5 Ground Loop - Bore Field Bore Field Circuiting 6 inch dia. Bentonite fill 138 ft 15 ft spacing

6 Ground Loop - Pond

7 Why is it good? Low Operating Cost Simplicity Low Maintenance Minimal Supplemental Heat Integrated Water Heating (low cost) No Exposed Outdoor Equipment Required Low Environmental Impact Level Seasonal Electric Demand Widely Applicable

8 VAV System Basics Add some fresh air at central unit Outdoor Air Cool all air at central distribution point Supply VAV Chiller / Boiler Schematic Chiller Boiler Exhaust Preheat Cool System circulates air between zones and central unit Return box Zone box Zone box Zone Zones change airflow for cooling and add reheat for heating

9 GX System Basics Geothermal Heat Pump Schematic A water loop moves heat between the heat pumps and the ground Ground Heat Exchanger HP HP HP HP Exhaust Supply Return Outdoor Air Ventilation air recovers heat from exhaust air, is preconditioned, and delivered to each HP Zone Zone Zone Heat pumps circulate hot or cold air as needed to a single zone

10 Low Operating Cost Water distribution vs Air distribution Water loop distributes energy throughout building» Ground loop circulates within building» Loop is insulated to avoid condensation Lower static pressure air» Heat pumps circulate air only within each zone» No central air handling unit needing high static pressure for control, coil and box pressure needs.» 0.3W/cfm vs 1W/cfm No reheat» No need to reheat circulation air to prevent overcooling.

11 Low Operating Cost Efficient heat pump operation with moderate loop temperatures Specify extended range heat pumps (32 F to 100 F) Specify high efficiency equipment ISO rating >14 Btu/wh similar components as air source 10 SEER unit Minimize water-side head loss Less than 12 ft at 3 gpm/ton Less than 10 hp/100 tons loop pump Properly size ground heat exchanger loop Size based on diversified heating or cooling load No setback avoids large startup peak loads

12 Low Operating Cost Efficient heat pump operation depends on loop temperature Loop size designed to limit extreme loop temperatures (35 85 F typical) Performance COP COP EER Loop Temperature EER

13 Low Operating Cost Efficient heat pump operation depends on loop temperature Loop size designed to limit extreme loop temperatures (35 85 F typical) Fond du Lac High School Pond Loop 700 ton system From Pond to HP From HP to Pond Daily Average Temperature 82 F 60 F F 20 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov

14 Low Operating Cost Moderate source temperature At 36 F Heating COP is 3.8 At 78 F Cooling EER is 17 Many hours of cooling at lower, more efficient loop temp.

15 Low Operating Cost New York Hotel Vertical Bore Field 350 ton system 100 Daily Average Temperature Outdoor Air F Ground Loop Supply X From Heat Pump Ground Loop Return + From Loop (to HP) 86 F Temperature (F) F 44 F 20 0 J J A S O N D J F M A M J J A S O N D J F M A M Loop Flow (1e5 gallons)

16 Low Operating Cost Need Annual Heating and Cooling loads to size ground loop Standard tools for zone capacity selection Ground loop sizing tools Need Assessment of soil conditions Thermal conductivity Drilling conditions Test $6K to $12K Gross estimates 150 ft to 200 ft of bore length per ton 15 to 20 ft bore spacing => 225 to 400 sq ft/ton 3 gpm per ton 25% propylene glycol in Wisconsin

17 Low Operating Cost Design Condition Efficiency Comparison CHW / 85 F 90 F EWT Component Tons kw Component Tons kw Chiller Heat Pumps Supply Fans MBTUH/3.26 kw) (200,000 4") Loop Pump 20 Return Fans 46 (25 hp) (200,000 1") Net Capacity 425 FPVAV Fans 80 Total Power 395 (200-1/4 hp) kw/ton 0.93 Condenser Fan 24 EER 12.9 (30 hp) Condenser Pump F EWT (25 hp) Component Tons kw CHW Pump 20 Heat Pumps (25 hp) 45.3 MBTUH/3.12 kw) Fan Heat Deduction -75 Loop Pump 20 Net Capacity 425 (25 hp) Total Power 625 Net Capacity 425 kw/ton 1.47 Total Power 373 EER 8.2 kw/ton 0.88 EER 13.7

18 Simplicity Distributed System Easy to operate Individual zone doesn t impact other zones Only loop pump speed changes with operating heat pumps Malfunctioning VAV box can drive entire system Problems typically isolated to a single zone Packaged Equipment Mount and attach to loop Only simple thermostat control needed Low operating costs are inherent in design Comfort is inherent in design Other system need controls to improve comfort and lower operating cost Design can complicate system and add cost $1-$2/sq ft for DDC Auxiliary systems, backups, heat exchangers

19 Low Maintenance Closed system System fluid treated and sealed Ground piping Fused Higher grade than natural gas lines Heat Pumps Regular filter changes Service expertise comparable to residential A/C Many compressors» Compressors designed for outdoor air-source heat pumps with defrost and higher compression ratios.» Application far less severe than design criteria Design for Maintenance Access

20 Low Maintenance

21 Minimal Supplemental Heat Heat Pumps can meet most loads Moderate loop temperatures Extended range heat pumps Limited by minimum inlet air temperature (50 F) Water to air heat pumps not used directly on large outdoor air loads. Can use water to water heat pumps Minimal mechanical space Central loop pump Ground loop entry to mechanical room Expansion tank Fluid treatment Zone equipment in ceilings or closets 1% vs 4% of total project floor area

22 Minimal Supplemental Heating Fond du Lac High School Boilers never used to supplement loop Most use during recovery from setback - discontinued Meets dedicated hot water loads - vestibules 2500 Boiler Run Time 2000 hours Boiler Stage

23 Water Heating Integration Dedicated water heating heat pump Provides 120 F water (COP > 3.0) Extracts heat from the loop Design Implication Ground loop sized for cooling can be smaller Must understand loads Consider recirculation losses Heat Pump Capacity / Recovery Ability Storage sizing Pilings Bores Cold Water Inlet Hot Water Recirc. 50 hp Loop pumps, variable speed HP HP 4 10 ton HPs 3,200 gal H.W. storage Ground HX Space Conditioning Water Heating

24 Water Heating Integration Water heating balanced loads and shortened loop length 20% = 20% cost reduction in loop. Water heating HPs were almost cost free!!! 400 w/o WH +2,520 & -890 MMBTU/yr Heat Transfer to Ground MMBTU w/ WH +2,000 & -1,430 MMBTU/yr Jun Jul Au Sep Oct Nov Dec Jan Feb Mar Apr May

25 No Outdoor Equipment Required Possible to have no exposed equipment Eliminate weathering wear Eliminate equipment vandalism Eliminates architectural consideration to hide / accommodate equipment Sloped standing seam roof possible Ventilation equipment can be indoor in a mezzanine

26 Low Environmental Impact GX VAV (MWh) (MWh) (Therm) Lights & Equip. 3,363 3,363 Space Heating ,036 Space Cooling Pumps Fans Total 4,693 4,612 92,036 Site Electricity Site Natural Gas Source Energy (MMBTU) (MMBTU) (MMBTU) VAV 15,741 9,204 56,425 GX 16,018-48,053 8,372-15% Fond du Lac High School Revised Model to Reflect Actual Operation

27 Low Environmental Impact VAV SO2 NOx CO2 lb/mwh ,926 Electricity MWh 4,612 4,612 4,612 lb/mwh 41,323 31,670 8,882,568 lb/mmbtu Natural Gas MMBTU 9,204 9,204 9,204 lb ,104,432 Total lb 41,328 32,590 9,987,000 GX SO2 NOx CO2 lb/mwh ,926 Electricity MWh 4,693 4,693 4,693 lb 42,050 32,228 9,038,939 Electricity Source Coal 74% Nuclear 20% Gas 1.5% Hydro 4.5% Difference lb ,061 2% -1% -9% Fond du Lac High School Revised Model to Reflect Actual Operation

28 Level Seasonal Electric Demand Monthly Peak Demand (kw) 2,000 1,800 1,600 1,400 1,200 1, Annual electric demand levels out with GX VAV GX - Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

29 Ventilation What is the best way to deliver fresh air? Central Condition fresh air with primary air Must coordinate fresh air fraction when total air flow varies Monitoring and controls OA amount driven by need zone with highest need Individual Zone Isolate ventilation load independent from comfort conditioning Heat recovery options Small uninsulated ducts Amount of fresh air to each space is known IAQ assured Zone level demand controlled ventilation

30 Dedicated Ventilation 3 hp 3 hp 4000 cfm office Total Heat Recovery Sensible Heat Recovery DX gas-fired makeup air unit Water-to-water heat pump Heat recovery heat pump Heat pipe DX electric makeup air unit FAN POWER 640 W wheel coil 3 hp 3 hp 1 hp 1.5 hp DX coil furnace 1.5 hp 1 hp HP 1.5 hp 1.5 hp hx coil 1 hp 1.5 hp HP coil 1.5 hp 1.5 hp Heat Pipe DX coil electric

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32 Dedicated Ventilation Often coupled with dedicated OA system Ensures proper ventilation rates in all spaces» OA ducted to each space Facilitates heat recovery» HPs have 50F limit on incoming air» Water-to-water heat pumps can temper air Minimizes duct size» reduced floor to ceiling height» construction cost savings Uninsulated duct» Ventilation air supplied at neutral conditions

33 DDC Two-Speed AHU Display

34 Sun Prairie Office (69 tons) Load Diversity Middleton Office (146 tons) Heating Cooling 800 Heating Cooling Hours 400 Hours Cooling & Heating Load (1 ton bins) Cooling & Heating Load (5 ton bins) Geneva Hotel (284 tons) Johnson City School (400 tons) Heating Cooling Heating Cooling Hours Hours Cooling & Heating Load (5 ton bins) Cooling & Heating Load (5 ton bins)

35 Heating/Cooling Load Summary Peak Hourly / 4-hr Cooling Loads: % of Installed Cooling Capacity Equivalent Full Load Hours Cooling Equivalent Full Load Hours Heating Normalized Cooling Loads Sun Prairie Office Middleton Office Geneva Hotel Johnson City High School 34 / 32 tons 82 / 74 tons 106 / 101 tons 234 / 219 tons 49% / 47% 57% / 50% 37% / 35% 58% / 55% 679 hours 965 hours 613 hours 466 hours 504 hours 869 hours 372 hours 318 hours 1.7 ton-h/ft 2 -yr 2.2 ton-h/ft 2 -yr 1.7 ton-h/ft 2 -yr 1.2 ton-h/ft 2 -yr

36 Load Diversity Loop flow varies with number of operating heat pumps. Most operation between 45% - 55% speed. Initial control anomaly caused operation at 90% speed.

37 Load Diversity Heat pump operation follows occupancy pattern Building peak set on sept 9 th with 121 HPs operating

38 Load Diversity Observed 121 out of 195 heat pumps operating simultaneously in cooling 10 to 50 typical

39 Electricity Use Weather Dependence HPs and Ventilation fans increase energy use with increased heating and cooling loads Minimal space loads near 50F

40 Implications of Load Diversity on Ground Loop Sizing ASHRAE loop sizing procedure shows loop length is mostly a function of peak loads Loop Length Reduction Factor Varying peak loads while holding annual and monthly loads constant Peak Load Diversity Factor

41 Project Costs Cost associated with assessment of new system Cost associated with learning Performance requires investment in ground loop Fond du Lac High School 403,000 sq ft, 700 tons HVAC $12.90/sq ft ($7,426/ton) Pond loop $665/ton, 12 acres, (720) 300 ft coils Evansville High School 181,000 sq ft, 300 tons HVAC $14.80/sq ft ($8,930/ton) Vertical bores $1,500/ton, (460) 100 ft bores

42 Project Costs 95,300 sq ft Iowa High School Gym heat only gas-fired furnace, Ventilation air heated with gas-fired furnace 3.9 MMBTUH Heat Pumps, Furnace $2.45/sq ft $1,100/ton Interior Piping $2.54/sq ft $1,150/ton Duct work $4.18/sq ft $1,890/ton Controls $0.67/sq ft $200/ton Balancing $0.09/sq ft $40/ton Pipe/Duct Insulation $0.68/sq ft $300/ton Vertical Borefield $2.38/sq ft $1,075/ton TOTAL $12.99/sq ft $5,755/ton

43 GX Characteristics Low Operating Cost Simplicity Low Maintenance Minimal Supplemental Heat Integrated Water Heating (low cost) No Exposed Outdoor Equipment Required Low Environmental Impact Level Seasonal Electric Demand Widely Applicable