BOAT

District Cooling tops today’s agenda in many countries around the world, including United Arab Emirates (UAE) in the Middle East, where constant high temperatures call for a tremendous need for district cooling, in commercial as well as residential buildings. A crucial part of such systems, that help control and monitor the amount of chilled water required to cool down a specific structure, is flow meters.

During the past 20 years District Cooling has become more economical, environmentally sound and energy efficient. Combined with the rising concern for climate and environmental issues, global demand for alternatives to individual air-conditioning systems has increased dramatically, creating a renewed interest for district cooling equipment. Although this is a worldwide trend, District Cooling has developed differently from country to country and from region to region. There are several reasons for this:

  • Varying energy policies, including national and international legal regulations that every country has to adhere to (eg The Kyoto Agreement)
  • Fluctuating local and global energy prices
  • Changing climate conditions (global warming, greenhouse effect, regional climatic conditions, etc).

District Cooling in the Middle East

In the Middle East, or more specifically in the UAE, the market for District Cooling is booming. Apart from the obvious factor that the constant year-round heat creates a demand for air-conditioning systems, numerous large-scale construction projects are currently being built or are on the drawing board, including hotels, office buildings, airports, etc. Such buildings often incorporate glass as an important design feature, heating up the indoor air which subsequently needs to be cooled down by massive airconditioning units. Another factor adding to the indoor heat is the excessive use of electronic equipment such as computers and printers. All these issues, however, can be directly addressed with District Cooling.

DISTRICT COOLING GRID

The District cooling measuring principle: a flow meter controls the flow of chilled water, while also measuring the consumed energy.

What is District Cooling?

District Cooling is a concept in which the production of chilled water is limited to only a few centralised locations. From these production sites, the water is distributed to customers in different buildings. When the water is delivered to a building, it circulates through a set of refrigeration coils. Fans blow air across these coils, cooling the air and putting it into circulation in the building’s air-conditioning system. Alternatively, cooling can be produced from cooled water circulating in the network by using absorption technology.

One District Cooling plant can satisfy the cooling needs of several buildings and customers, providing a variety of benefits, both qualitative and economic. The qualitative advantages are perceived in terms of better comfort through a much better control of the internal temperature in buildings, better reliability and maximised convenience. The economic benefits are easy to identify. Not only is District Cooling extremely cost efficient, but the associated environmental advantages are also significant: a 50% energy saving means considerable reductions in power generation and production of CO2, which are the major contributors to global warming. District Cooling uses environmentally friendly refrigerants in a contained and controlled environment, which, combined with rigorous health and safety standards, means less potential damage to the ozone layer.

These benefits are well aligned with the goals of the Kyoto Agreement, which prescribes energy reduction by scaling down the use of energy inefficient split units, which are often utilised in traditional air-conditioning systems.

Eyes of the process

For an air-conditioning system to work properly, the processes involved have to be constantly monitored. One important focus in this context is flow meters. They are pivotal in ensuring precise system and process measurement and performance, especially for industrial billing purposes. Although several manufacturers make flow meters, only a few are total solution providers, one of them being Siemens. The company is involved in all segments of the district cooling industry by supplying integrated electrical, IT and automation and drives solutions. Offering a “Totally Integration Automation” solution, Siemens has its eyes on the process in District Cooling.

Flow metering in District Cooling

Flow meters are placed in strategically important locations, enabling enhanced procedure control, automation and efficiency of residential as well as industrial installations. When it comes to customer billing, flow meters are particularly important in that they measure the chilled water usage that customers are billed for.

Metering chilled water basically consists of measuring the water flow and the temperatures in the supply and return pipes. This data is sent to an energy meter unit (integrated or stand-alone) that computes the absorbed cooling energy as the product of Volume x Δt x k-factor.

In general, cooling systems are characterised by a relatively small difference between supply and return pipe temperatures; supply temperatures usually range from 4OC to 8OC (from 39OF to 46OF) and a return between 12OC and 18OC (54OF and 63OF). In order to produce the necessary cooling power at such low temperature differences, the upper part of the nominal measuring range of the flow meters in cooling systems will typically be used, whereby the flow meters’ uncertainties are maintained at a minimum.

Since the water flow in District Cooling systems can be measured by both mechanical and electronic flow meters based on different measuring principles, it is important that decision-makers familiarise themselves with the advantages and disadvantages of the different meters and principles.

Choosing the right flow meter

Generally speaking, cooling systems have a high, constant water flow over long periods and therefore it is important to choose a flow meter that will not be “worn out”. Electronic meters have no moving parts, which makes them a good choice for District Cooling applications. In addition, they are designed with resistant materials, have long lifetimes, and are reliable and robust.

Ultrasonic flow meters are very suitable for energy measurement in the cooling industry. The Sitrans FUE1010, a clamp-on ultrasonic energy meter developed especially for energy metering, is a very cost-effective solution. It is available in a portable and a fixed installation version. As with any other Siemens clamp-on meter, it is not necessary to cut the pipe or shut down operations to install it; the transducers are quickly and easily mounted on the outside of the pipe. The bidirectional meters offer a pair of 1000 Ω resistance temperature detectors (RTDs), ensuring accuracy in chilled water and the choice between one or two channels. The clamp-on meters can measure on both the heating and cooling supply pipe, using only one meter. In addition, it has a dual mode option that enables the meter to automatically change between transit time and Doppler measurement. This allows it to detect foaming conditions often caused by glycol in the chilled water, which goes unnoticed. In addition, the built-in auto zero functionality ensures zero drift compensation and advanced user-settable diagnostic capabilities.

Another ultrasonic clamp-on meter that can be used for District Cooling is the versatile FUS1010. Since it solely measures flow it is a reliable solution for customers that would like to combine an existing temperature reading with flow to calculate their energy consumption.

Siemens also offers the ultrasonic Sonokit, which is a simple, accurate alternative to traditional flow meters because it can be retrofitted onto existing pipes. The installation can either be made on an empty pipe or on a pipe under pressure (hot-tap installation). The Sonokit has wetted transducers that are in contact with the media, assuring good accuracy, performance and stability.

Another flow technology readily applicable to District Cooling systems is based on the magnetic inductive principle. The Sitrans F M MAG 5100 W Siemens is designed for water applications and is made of highly resistant Hastelloy C. It is precise with 0.25% accuracy. Although the MAG 5100 W is available in sizes ranging from DN 25 to DN 1200 (1” to 48”), the cost-benefit aspect makes it most efficient when installed on smaller pipe sizes.

The SITRANS F M MAG 5100 W is custody transfer approved, which makes it appropriate for billing purposes. This is especially valuable in District Cooling where custody transfer is pivotal, eg for private billing. Another feature of the flow meter is the calibration report, which certifies the installation and proves the performance of the product.

If an energy meter is needed, Siemens has the integrated Sitrans FUE950 energy calculator. It is a battery or mains-powered universal custody transfer device designed for use in hot water, chilled water and cooling/heating applications. The calculator has a modular construction, which means that it can be fitted with optional modules.

On-site verification

In accordance with current District Cooling regulations and legislation, verified energy flow meters either have to be dismounted or controlled by random sampling at intervals of 5 or 6 years. In a situation where it is time-consuming and expensive to uninstall a meter, it can be beneficial to make an on-site verification of the flow meter instead.

One versatile and easy-to-use verification option is the Sitrans FUE1010 portable HVAC Check Metering Kit. Basically, the meter has the same capabilities as the dedicated FUE1010. There are, however, a few important differences. First of all, the kit has been developed especially for verifying the accuracy and performance of any brand or type of energy meter. It measures practically all conductive or non-conductive clean or moderately aerated liquids or liquids with suspended solids. This basic feature makes the kit capable of verifying the performance of meters based on any existing flow measurement principle: electromagnetic, ultrasonic, orifice, rotary piston and coriolis. Secondly, the kit is delivered in an all-inclusive rolling case with a telescope handle that holds all the equipment needed to conduct performance and verification tests, including cables, high precision transducers, flow computer, certificate of “Intrinsic Calibration”, etc. Lastly, the portability of the kit makes it easy to carry from one measuring point to the other.

Another verification option is the Verificator, which is a portable measurement device used to verify the performance and accuracy of magnetic inductive flow meters. The verification takes place while the meter is in operation, making temporary shut-downs unnecessary. The verification test is performed in less than 15 minutes and the customer receives a verification certificate right after the test has been finalised. The Sitrans F M Verificator is designed to ensure long-term stability and accuracy, it is sent for external verification once a year and each Verificator’s history is documented and traceable. With regards to accuracy, the Verificator can determine if a specific flow meter is performing as precisely as the day it was built and it can verify this with 99.99% accuracy.

Flow meters enhance the benefits of District Cooling

As shown throughout this article, the growth potential for District Cooling is significant. For climatic reasons, the need for cooling in the Middle East is huge: high temperatures all the year round make cooling essential, heat needs to be removed from large structures such as hotels and office buildings and the high rate of construction are all factors that increase the need for District Cooling.

Some of the advantages of District Cooling are perceived in terms of better comfort, better reliability and maximised convenience. Additional advantages are:

  • Better quality of cooling
  • Maximum cost-efficiency
  • Capital cost elimination
  • Space saving benefits
  • Decrease in noise pollution
  • Environmentally friendlier than other air-conditioning options
THE VER

The Verificator enables on-site verification of magnetic inductive flow meters: The Verification takes place while the meter is in operation, and thus temporary shut-downs become unnecessary.

The use of flow meters is crucial in District Cooling. As the number of District Cooling applications have increased, so has the need for metering. By measuring the flow throughout a cooling system, Sitrans F flow meters give you total control over a system, enabling significant cost reductions. The flow meters offered by Siemens such as the FUE1010, FUE1010 HVAC Check Metering Kit, Sonokit, the MAG 5100 W and the FUE950 are a good choice to take full advantage of the possibilities that District Cooling offers.