District Cooling Best Practices Piping Systems

Transcription

1 District Cooling Best Practices Piping Systems International District Cooling Conference January 14-17, 2007 Abu Dhabi, United Arab Emirates Bryan Kleist

2 Agenda Chiller Water Piping Materials Pipe Insulation Isolation Valves Service Pipes System Pressure Control Variable Primary vs Primary/Secondary

3 Chilled Water Distribution System Piping Materials Best Practice Materials: Welded Steel Ductile Iron HDPE

4 Steel Piping Characteristics Toughness High pressure rating High velocity limit Thrust blocks not required (nor anchor blocks in most cases) Pre-insulated steel piping system can last forever when properly installed and operated Pre-insulated steel piping is available with integrated leak detection system

5 Pre-insulated Steel Piping For insulated steel piping, a pre-insulated piping system is recommended Polyurethane insulation Polyethylene or fiberglass jacket Does not require cathodic protection Double seal or air-tested field joint insulation system recommended for leak-tight joints Procure from vendor that certifies a fully bonded system

6 Ductile Iron Piping Characteristics In many areas, soil conditions are not considered corrosive to ductile iron Mortar lining is very corrosion resistant Installed cost is usually lower than for welded steel piping systems High pressure ratings available Velocity limitation with mortar lining Thrust blocks required for unrestrained (push-on) jointing system

7 HDPE Piping Characteristics Effectively corrosion proof Considerably tougher than other plastic piping systems Flexibility allows piping to route around obstacles without requiring fittings in many cases Properly executed butt fusion joint is as strong as the HDPE pipe itself Pressure ratings are limited, especially in larger sizes

8 Steel Piping Good choice of material: Value tough and leak-tight piping system Insulation is required Expect to be able to maintain clean water in chilled water distribution system Want to be able to operate at high velocities Consider different material: Speed of installation is a priority Insulation is not required

9 Ductile Iron Piping Good choice of material: Soil conditions are not corrosive to cast iron Insulation is not required Do not expect to be able to maintain clean water in chilled water distribution system Minimizing first cost is a priority Consider different material: Pipe corridor available does not have adequate room for thrust blocks Want to be able to operate at high velocities

10 HDPE Piping Good choice of material: Lower pressure systems HDPE piping gets very expensive at higher pressure ratings Lots of small directional changes that can be accommodated by natural flexibility of pipe For smaller sizes, where HDPE is more cost effective For water crossings (channel, river, etc) Consider different material: Want the flexibility to increase system design pressure in future For pipelines requiring a large number of fittings In a region where labor costs are low

11 Pipe Materials for Seawater Intake & Outfall Piping HDPE Ideally suited for submarine deployments Joint fusion on shore and then pipe deployed by controlled submergence with pipe weights Pipe can be laid directly on sea floor Toughness GRP More cost-effective than HDPE for large sized terrestrial buried seawater pipes Larger sizes available

12 Pipe Insulation 1) Estimate ground temperature at pipe bury depth through the year 2) Prepare heat gain calculations to determine if energy & capacity loss economically justify insulation 3) Consider supply temperature rise against customer supply temperature requirements

13 Example of Ground Temperature Calculations 105 Estimated Average Ground Temperatures (at depths by month) Temperature (F) Jan-06 Feb-06 Mar-06 Apr-06 May-06 Jun-06 Jul-06 Aug-06 Sep-06 Oct-06 Nov-06 Dec-06 Jan-07 Month of Year Surface 2 Ft of Bury Depth 5 Ft of Bury Depth 10 Ft of Bury Depth

14 Example of Supply Temperature Rise Calculations 2.50 Distribution System Supply Temperature Increase For Example System at Part Load 2.25 Supply Temperature Increase (ºF) Pipes 18" and larger Pipes less than 18" No Insulation Insulation on all pipes Insulation on pipes less than 18" Piping Distance from District Cooling Plant (ft)

15 Steel Pipe Insulation Pre-insulated piping system offers best chance of long-term leak-free service Field-applied insulation has greater risk of leaks Considerations re field-applied insulation Groundwater Insulation method Contractor skill, quality, experience Installation monitoring by owner

16 Isolation Valves Direct Buried Direct buried valves eliminate valve chambers and flanges a potential leakage point Weld-end ball valves best solution for direct buried valves for most sizes Available pre-insulated only standard pre-insulated field joint kits are required Downside must dig up street to get to valve but should not be required

17 Isolation Valves Direct Buried Ball valves expensive in large sizes Metal seated, weld-end butterfly valves used in Europe for pipes over 600mm (24 ) Downsides to metal-seated butterfly: Shut-off is not as tight as for ball valves Risk of debris collection at seat impeding shut-off

18 Isolation Valves Direct Buried Mechanical actuation via shaft to surface above valve Hydraulic actuation system available gets access to valve actuator out of the street

19 Direct Buried vs Valve Chambers Regions of the world with cheaper labor costs valve chambers with butterfly valve are more cost-competitive In Middle East, for example, valve chambers are generally: More cost-effective for shallow-buried installations, especially for large pipe sizes Less cost-effective for deeper-buried installations, especially for smaller pipe sizes

20 Direct Buried vs Valve Chambers Middle East Cost Comparison 12 Cost Comparison Between Direct Buried Ball Valves and Valve Chambers with Butterfly Balves For SHALLOW Pipe Bury Depth 10 Direct buried, preinsulated, weld-end ball valves Valve chamber with flanged butterfly valves Cost (relative) Valve size (DN)

21 Direct Buried vs Valve Chambers Middle East Cost Comparison 40 Cost Comparison Between Direct Buried Ball Valves and Valve Chambers with Butterfly Balves For DEEP Pipe Bury Depth Direct buried, preinsulated, weld-end ball valves Valve chamber with flanged butterfly valves Cost (relative) Valve size (DN)

22 Service Pipes With high level of confidence in securing future customer install service stubs when main pipeline is installed Moratorium on work in streets may require installation of branch or service stubs so that customer opportunities are not missed Moratoriums common for greenfield developments which are especially typical for systems in the Middle East

23 Service Pipes Hot Tapping Hot tapping of chilled water piping is possible offers following benefits: No interruption of service to existing customers Eliminates costly and time-consuming draining of the main pipe Defers capital outlay until customer contract is secured Cost effective enough in small sizes to plan for hot tapping even if customer connection is highly probable.

24 Service Pipes Hot Tapping For all-welded steel system, hot tapping with branch welded to main is preferable to mechanical clamp fitting. Welded hot tap methods: With weld-end ball valve Sluice plate method Sluice plate method helpful when space is limited

25 System Pressure Control Open thermal storage tank as accumulator good practice for system pressure control Optimal only if can be: Constructed tall enough to meet static pressure requirements Constructed at a hydraulically desirable location Another benefit open storage tanks offer ability to accommodate large system fillings while maintaining system pressure requirements.

26 Variable Primary vs Primary/Secondary Variable primary flow through chiller evaporators Offer first cost and operating cost savings over primary/secondary arrangement Special considerations for large district cooling plants: Plants with a large number of chillers in parallel operating cost savings, on percentage basis, will not be as high as for typical building plants Impact to available distribution system dp must be considered against potential first cost savings

27 Thanks for your attention! Bryan Kleist Phone: