Transcript
Low Delta T ( ∆T) is Far Too Expensive for District Cooling Eric M. Moe IDEA Annual Conference Scottsdale, Arizona June 2007
Common (and Expensive) Myths Energy – Capacity – Complexity - Comfort
Myth: Without decoupling buildings or indirect connections, existing (low ∆T) cooling coils are incompatible with the new (high ∆T) plant. 12F (6.7C) ∆T 10F (5.6C) ∆T
1000 ton customer 45/55F coils (7.2/12.8C)
16F (8.9C) ∆T chilled water plant 41/57F design (5.0/13.9C) 41F(5.0C)
1500 ton customer 44/56F coils (6.7/13.3C)
Reality: Colder water and better control will deliver greater than design ∆T at peak and part load Energy Labs Coil 5WC-0 806-54x160-A36/6C 80 ) s n o t (
70 10.0F (5.6C) ∆T
60
50 d
41F (7.2C) EWT
16.2F (9.0C) ∆T
a o L 40 g n 30 i l o o 20 C
45F (5.0C) EWT
19.8F (11.0C) ∆T
Colder CHWST to Coil Increases ∆T ∆ T Rises Above Design at Part Load
10 0 0
50
100
150
Flow Rate (gpm)
200
250
Avoid the Expense: Design with cold water and better control to achieve high ∆T at cooling coils • Design the chilled water plant and distribution for high ∆T despite low ∆T cooling coils in buildings • Simplify customer interconnections – Direct connect if possible, HEX if required – Maintain the supply water temperature to coils – Avoid return water temperature control
• Rely on (high quality) pressure independent control – Achieve high ∆T performance across coils – Eliminate balancing, even as a system expands
Myth: System performance (including ∆T) can be optimized at the building interface alone LAT
LAT
VFD (w/ 2-way & balancing valves) Building level return water temperature control Decoupling (blending)
T
HEX (indirect connection) T
Flow limiter (balancing)
T
T
Reality: Low ∆T at coils commonly leads to rising supply water temperature which adversely affects performance for the utility and its customer 82
28 Wet Bulb Outside Air Temperature
) 72 F g e d ( 62 e r u t a r e p m52 e T
22 )
17
Supply Water Temperature To Coils
42
11
6 Supply Water Temperature To Building
32
0 Two Weeks in July 2007
C g e d ( e r u t a r e p m e T
Avoid the Expense: Achieve high ∆T at coils to reduce total energy use, retain customers, simplify systems, and get paid • For the Chilled Water Utility – Re-capture lost latent cooling revenue • Eliminate low ∆T at the loads • Maintain low chilled water supply temperature to coils
– Acquire, satisfy, and retain customers • More comfort, greater efficiency, less equipment, lower costs
• For the Connected Customer – Minimize complexity • Direct connections, HEX if required, no balancing
– Reduce pump and fan energy consumption • Higher ∆T in building, maintain low supply air temps • Remove pumps if not required
Myth: District cooling utilities can’t control what customer’s choose to do within their buildings.
• • • • • • •
Lowest first cost design Insufficient maintenance, dirty coils Bypasses, 3-way valves, C/S pumps Bad pump, pipe, and valve sizing practice Minimal engineering, oversized equipment Poor chilled water flow control Low leaving air temperature
Reality: District cooling utilities may develop rate structures that influence customer design and performance
$/ton-hr $0.22 $0.21 $0.20 $0.19 $0.18 $0.17 $0.16 $0.15
∆T
(°F) ≤13 14 15 16 17 18 19 ≥20
∆T
(°C) ≤7.2 7.8 8.3 8.9 9.4 10.0 10.6 ≥11.1
gpm/ton 1.85 1.71 1.60 1.50 chilled water plant design 1.41 1.33 1.26 1.20
It may take a carrot to add a stick to change existing long term contracts!
Example: ~ 25,000 ton commercial plant with ongoing (expensive) low ∆T issues • New plant designed for 10°F (5.6°C) ∆T - coils have 15°F (8.3°C) ∆T capability with 40°F (4.4°C) supply • Direct customer connections in original design, no decoupled buildings or heat exchangers • Additional chiller added after startup due to low ∆T performance in buildings • Utility now has a rate structure that penalizes customers with poor ∆T performance • Some customers are adding heat exchangers to try to deal with low ∆T • Rising supply water temperature is creating comfort issues in customer buildings
What to Do: Explore common low ∆T issues relative to coil, distribution, and plant capability • Low return temperature (to the plant) • High supply temperature (to cooling coils) • Where does the excess water go? – – – –
Overflow running chillers Operate additional chillers Blend return water with supply Quickly deplete TES capacity
What to Do: Use ARI certified software to fully understand coil capability at peak and part Load Energy Labs 5WC-0 806-36x160-A14/10C Design Conditions (16.0F, 8.9C ∆T)
120%
Actual Peak Load (21.6F, 12.0C ∆T)
100%
) % ( d a o L g n i l o o C
80% 60%
explore what happens with changes to the entering water and leaving air temperature conditions
40% 20% 0% 0%
20%
40%
60%
Coil Design Flow (%)
80%
100%
What to Do: Assess the economic benefit of correcting low peak and part load ∆T Example: 12,000 Ton (Growing) Level 1 Trauma Center “10°F (5.6°) ∆T Coils with a 16°F (8.9°C) ∆T Plant” – – – – – – – – – –
Retrofit project Pressure independent control (DeltaPValves), no new coils Reduced gpm/ton by over 60% raising part load ∆T from 7°F (3.9°C) Removed building pumps and bridges Increased peak load ∆T from 12 to 16°F (6.7 to 8.9°C) 7,082,381 kWh annual savings (equivalent lbs CO 2 reduced) 53,631 kW reduction at peak (campus has CHP and reverse metering) Increased available system capacity by ~ 3000 tons Improved system reliability and comfort control Eliminated waterside balancing requirements $1,260,000 investment ($105/ton) $708,238 annual savings (plant energy alone) 1.78 years simple payback
What to Do: To drive good design, create chilled water contracts that vary with ∆T performance Example: 4,500 Ton District Cooling (Airport) Customer “Penalties in contract for less than 18°F (10°C) ∆T” – – – – – – – –
New construction project Pressure independent control (DeltaPValves) at coils 38/56°F (3.3/13.3°C) chilled water plant design Thermal storage (ice) is fully utilized to minimize peak load Cold water maintained all the way to cooling coils Customer achieves 20-24°F (11.1-13.3°C) ∆T at all loads Distribution managed with a single secondary pump in central plant No excess pumping, piping, control, balancing, or heat transfer equipment in the terminal buildings
Questions?
Eric Moe Flow Control Industries
[email protected] Office: 425-483-1297 Cell: 206-890-3266