Steam Cooling Systems
for
Buildings Explained
Con Edison
AKF Engineers
Spring 2008
Joseph Rubino, PE
Steam Seminar
When evaluating a Refrigeration Plant
Design Concept the following issues
should be considered:
¾ Peak Cooling Load
¾ Cooling Load Profile
¾ Alternate fuel Sources
¾ Redundancy
¾ Reliability
¾ Operating Cost
¾ Maintenance Costs
¾ Operating Staff and Owner’s Input
Various options are available:
¾ Electric
¾ Steam
¾ Gas
¾ Thermal Storage
¾ Hybrid Systems
¾ Tri-fuel Systems
¾ Combined Heat Power
Today we will discuss on the benefits of Steam Refrigeration
Plants, Hybrid Plants, and Tri-fuel Plants.
Steam, electric and gas have proven to be reliable energy
sources in NYC.
The Advantage of installing “Hybrid or Tri-fuel plants” are
as follows:
¾Built-in utility redundancy
¾The plant does not rely on one energy source
¾Operator flexibility
¾Ability to benefit from “time of day” rates
¾Can avoid or reduce electric demand charges
Steam Turbines
Steam turbines have a long and proven history since their
initial practical development in the late 19th century:
¾ Provide reliable shaft horsepower
¾ Widely used in the industry
¾ Versatile prime mover technology
There are several types of steam turbines:
¾ Condensing
¾ Non Condensing (Back Pressure)
¾ Single Stage
¾ Multi-stage
Steam Turbines
A steam turbine is an energy conversion device.
Steam or thermal energy is converted to mechanical
energy with the help of a high speed turbine rotor and
final conversion to refrigeration by means of a
compressor.
Turbine technology has advanced significantly in recent
years with upgrades to the blade geometry, materials,
bearings, seals and controls.
The equipment manufacturers have automated the control
systems to optimize turbine speed control with the vane
position which improves the overall system performance and
efficiencies.
Steam Turbines
Improved performance translates to an increased heat rate or
thermal efficiency.
Steam consumption for multi-stage turbines:
¾8.5 lbs/ton-hr – 10.5 lbs/ton-hr at full load
¾6.5 lbs/ton-hr – 8.5 lbs/ton-hr at part load or IPLV
System efficiencies can be further increased by using heat
recovery equipment.
Steam Turbine Design - Components
Rotors
¾ Rotor assembly consists of all parts which rotate
excluding the coupling.
Steam Turbine Design - Components
Buckets
¾
Turbine blades (buckets) are
normally 403 or 420
stainless steel.
¾
Some blades are made from
Titanium. (light weight, high
strength, but difficult to
machine).
¾
Lower stressed blades are
made from stock drawn to
foil shape (Drawn Blades).
Absorption
Chillers
¾A thermal compressor consists of an absorber, a
generator, a pump, and throttling device
¾The refrigerant used is actually water
¾Salt generally lithium bromide drives the process
¾Heat is used to separate two fluids
¾Fluids are combined together in a vacuum environmental
and remix at low temperature
¾Water experiences phase change and causes the cooling
effect
Absorption
Chillers
Compared with mechanical chillers, absorption chiller have a
low coefficient of performance. (COP = Chiller output /heat
input).
However, absorption chillers can substantially reduce
operating costs because they can be powered by low pressure
steam or low grade waste heat.
Single stage or single effect absorption chillers provide a
thermal COP of 0.8 (IPLV) and require approximately 18 lbs/tonhr of 15 psig steam.
Two stage or double effect absorption chillers provide a thermal
COP of 1.3 (IPLV) and require approximately 10 lbs/ton-hr of 125
psig steam.
A single effect absorption
chiller means that all
condensing heat cools and
condenses in the
condenser. From there it is
released to the cooling
water.
Single Effect
Absorption
Refrigeration Cycle
A double effect absorption chiller has a higher efficiency and
divides the generator into a high-temperature and a low
temperature generator.
Double Effect
Absorption
Refrigeration Cycle
TYPICAL WATER-COOLED CHILLER
EFFICIENCIES
CHILLER TYPE
*INTEGRATED PARTLOAD VALUE (IPLV)
Steam/Hot-water
Single Stage Absorption
0.8 COP
Steam Two-stage
Absorption
1.3 COP
Steam Turbine Centrifugal
1.8 COP
*IPLV’s are calculated according to Air-conditioning
and Refrigeration Institute Standards 560-2000 and
550/590-1998.
HIGH EFFICIENCY
COP Comparison
2.5
IPLV
1.8
2
COP
1.5
1
IPLV
1.3
0.5
IPLV
0.8
0
0
10
20
30
40
50
60
70
80
Load
Double effect absorber
Steam turbine
Single effect absorber
90
100
Combined Heat and Power:
Vertical Steam Turbine Generators
Microsteam® Turbine Generators (STG)
A typical installation (one microsteam turbine) can generate
approximately 275 kw, with a 12,000 lbs/hr steam consumption
and a reduction in pressure from 150 psig to 15 psig.
Multiple microsteam® turbines can be manifolded together to
generate additional power providing the steam capacity is
required based on the steam load profile for the facility.
The microturbines® are typically piped in parallel with the
pressure reducing valve stations (PRV).
Combined Heat and Power:
Vertical Steam Turbine Generators
Microsteam® Turbine Generators (STG)
The steam flow is diverted to the microsteam turbine in lieu of
the PRV station. The high pressure steam is utilized to turn the
high speed turbine rotor. The transfer of energy is recovered in
a gear box which is connected to a generator which produces
electricity and distributed to the facility.
The 275 kw skid mounted power package measures 34” width x
42” length x 78” height.
The low pressure steam from the turbine outlet can be utilized
for absorption chillers, heating coils, domestic hot water
preheaters, process heating applications, etc.
Design Considerations for High
Pressure Steam Systems
¾Minimize the rate at which steam condenses
¾Design the system to handle condensate
¾Use air vents, separators, and steam traps
¾Pitch steam piping in direction of steam flow
¾Steam must be trapped and removed before it can
accumulate
¾Proper trap selection is important
¾Good design practice is a prime consideration
Design Considerations for High
Pressure Steam Systems
¾All piping, pressure reducing value stations (PRV’s) and
related components must be designed in accordance with
the latest Con Edison standards.
¾New York City Building Code.
¾ASME B31.1.
¾All welds for high pressure steam systems are subject to
radiographic examination.
Design Considerations for High
Pressure Steam Systems
¾The piping system must be designed to allow for thermal
expansion.
¾Maintain allowable stress ranges during expansion and
contraction cycles.
¾The forces on equipment and turbine nozzles must be
designed in accordance with acceptable limits.
¾Acceptable limits for turbine nozzles are based on NEMA
standards.
In Summary
¾Con Edison steam is a viable solution for heating and
cooling systems.
¾If properly designed can be very efficient and cost
effective.
¾(45% - 55%) of Con Edison steam is a by-product of
power generation.
¾Use of Con Edison steam helps to reduce the carbon
footprint.