Metering technology in Heating System
The normally answer will be the steam side since this side providing the usage energy. But our answer is the opposite measure the condensate can be provide the most accurate results.
Saturated steam or superheated steam and this two status not always stay wher they are they can transfer to each other due to some reasons, like superheated steam may become to saturated steam due to heat lost after long way transfer. We also need to faced with compressibility/density changes due to pressure/load variances and operating ranges that have extreme variations depending on the time of the year/season. Considering above factors and measurement technologies, there’re very limited to offer a reliable, accurate measurement solutions for most of manufactures.
Vortex meter which are popular and have very mature technology in steam measurement. Briefly to say is the bluff bar of vortex shedding start to create vortices when flow passes, and sensing technology detects the vortices and terminal board will reflect this relations and turn in to flow rate. Based on this vortex meter have a maximum and minimum velocity range
Vortex meters are very linear and repeatable to ±1.0% of reading accuracy with a typical ideal turndown range of 20:1(normally marked on the market) that can meet most measurement in steam area.
How do we select the right vortex meter to match with the pipeline?
If the pipeline is DN100, should we just select a DN100 vortex type flow meter? Well, it’s not that simple. In order to properly size a vortex meter you need to know the max/min flow rate and also the working temperature and pressure. Technically a vortex meter should also detect the pressure and temperature during working is an ideal module for steam measurement especially for superheated steam application.
Let’s swap the factors involved in measuring energy usage from steam side of the system:
1)Generally, to measure steam side as its the usage heating medium.
2)Steam it’s a medium hard to measure with high accuracy and turndown due to its nature.
3) Heating loads can vary widely with seasonal requirements which making the flow range extremely large.
4)Vortex type flow meter is the ideal module for application because of it’s accuracy, linearity and reliability.
5) Limitations n vortex meter technology is the turndown ration.
Knowing there such limitations in the steam measurement why we not select to measurement on Condensate side?
Compared with steam, Condensate provide a measurement with more reliability and turndown, don’t need to worry about excessive temperature and density changes. Measurement becomes more simplified and available to have a wide range to technology. However, there still have some measurement issues with the application.
First, considering the reliability should except all mechanical volumetric flowmeters. Due to the nature of condensate makes us to choose technologies such as vortex, ultrasonic and magnetic which provide accurate and reliable measurement and complete free of any moving parts.
Second, considering the accuracy and turndown we can remove Pitot tubes(differential pressure meters) from the list. As the accuracy at low flow become an issue at a low flow rate are further complicated by the square root extraction of the error required to convert DP (differential pressure) into flow rate measurement.
There also have Ultrasonic and Magnetic technology for option. Speaking of Ultrasonic, by measuring properties, preferably higher speeds, accurate time-of-flight measurements are made. This limits the low end speed to approximately 1.0 ft/sec to maintain accurate measurements. This is acceptable for pumping condensate, but it is definitely not suitable for gravity condensate, which can easily approach 0.01 ft / sec. Magnetic meter can for most of liquid purpose that medium is electrically conductive with 500:1 turndown capabilities.
Let’s swap the factors involved in measuring energy usage from Condensate side of the system:
1)Due to the nature of the condensate (liquid), it is a medium that is easier to measure, with high reliability, accuracy and adjustment ratio.
2) Heating loads can vary widely with seasonal requirements which making the flow range extremely large.
3) The most suitable model is Magnetic but required the medium be electrically conductive.