District Energy - 2010 Third Quarter

porate both transit-time and Doppler capabilities, enabling users to make all required measurements with one unit.

Multiple Applications

Since they can be installed anywhere along district energy distribution pipelines, clamp-on ultrasonic flow meters have the flexibility to be used to balance a hot or chilled-water system, improve chiller performance, indicate direction of flow, or measure thermal energy use.

These meters can be used to balance a hot or chilled-water system, improve chiller performance or measure thermal energy use.

Balancing Flows

Prior to clamp-on flow meters and transit-time technology, balancing flows throughout a building was done by only reading flows at the circuit-balancing valve. The balancing valves provide pressure taps, and a differential pressure manometer is used for proportional flow correlation. One disadvantage of balancing valves is that they are not always located on the line where critical measurements need to be made.

Portable clamp-on meters, however, may be used anywhere on the line, and dual-channel models are able to measure two pipes simultaneously. These units can be used to balance systems as well as to verify a hot or chilled-water system’s overall performance. Using measurements taken at various locations along the heating or cooling loop, system operators can ensure that energy is distributed properly. When this is the case, systems often find they can reduce their hot and chilled-water production – saving energy and operating costs, as well as reducing the need for additional maintenance and/or equipment.

In district cooling plants, channel one can measure the chilled water while channel two measures condenser water.

This information enables operators to regulate the flow to design conditions. In cases where a main pipe is not accessible, measurements may be taken on two branches, which the meter can then add to get the total flow in the main. For a two-branch system, flow can be calculated by measuring main flow and subtracting the flow of branch one from that of branch two. Another example would be measuring the primary, secondary and tertiary flows of a decoupled chiller system. The clamp-on technology can be used very effectively to indicate direction and flow rate of the decoupled crossover connection.

In hot water district heating systems, clamp-on meters can measure the output flow of two boilers simultaneously to balance them. They can also measure the recirculation loop on boilers to ensure that minimum design flow requirements are met; flow below the minimum design standard can possibly cause damage to the boiler.

Improving Chiller
Performance

In addition to balancing systems, the clamp-on meter’s ability to measure two pipes simultaneously makes it useful in assessing how well a chiller/heat exchanger is performing and whether work needs to be done on it to improve efficiency. This is done by measuring the condenser and evaporator flows and temperature using clamp-on transducers and resistance temperature detectors in the flow meter.

In the Siemens Sitrans FUE series of clamp-on meters, the flow and temperature measurements, along with a kilowatt input, provide operators with a coefficient of performance and energy efficiency ratings. The data can be used to compare chiller performance before and after any maintenance is done, which will indicate how much improvement has been made.

Measuring Thermal
Energy Use

Clamp-on ultrasonic flow meters can also be used to measure hot or chilled-water use for billing purposes. District energy plants can meter the

consumption of customer buildings, and building owners can submeter their tenants’ thermal energy use as well, by floor. The advantage to billing based on each customer’s or tenant’s energy use (as opposed to by square footage or apportionment) is that it allows their individual consumption levels to be projected – which better enables energy consumers to become aware of and curb unnecessary energy use.

In these instances, a permanent revenue-grade unit would be used that measures the flow rate along with the supply and return temperature to calculate Btus. This type of meter is wall-mountable and provides an analog or digital output of Btu or tons. A portable clamp-on meter can be used in addition to verify the accuracy of permanent meter readings.

The temperature sensors are avail-
able as clamp-on or insert types and are
precision-matched to 0.02 degree F pro-
viding a highly accurate delta T reading.
Thermal energy measurements are eas-
ily made as the flow and temperature
elements are ‘nonintrusive.’
With their versatility in these vari-
ous applications, clamp-on ultrasonic
flow meters can be useful in commis-
sioning or recommissioning build-
ings or district energy systems, as
well as in helping buildings achieve
LEED® (Leadership in Energy and
Environmental Design) Green Building
Rating System™ certification. In the
LEED system, the measurement of
hot and chilled-water system flow is
required for a building to earn points
in the Energy and Atmosphere –
Measurement and Verification credit
category (EAc5) for both existing and
new construction. Buildings must
provide measurements demonstrat-
ing chiller efficiency, boiler efficiency,
flows, building usage, and the amount
of energy used to produce heating or
cooling (kilowatts per ton).