Variable speed drives key to district heating expansion
In Sollentuna, as in the rest of Sweden, greater consideration for the environment, plus rising electricity and oil prices, has led to more and more people wanting to connect their property to the district heating network. Development and expansion of capacity is taking place at a tremendous rate to meet the rising demand.
A total of 318 properties signed up over the course of 2005. By the end of 2006, almost all the blocks of flats in the municipality and just over 2600 single-family dwellings had also been connected. In Sweden district heating now accounts for around half of all heating in homes and business premises.
The company Pumphuset is also based in Sollentuna, and for many years it has installed and maintained pump controls in the local heating, water and wastewater plants. Pumphuset works with all manner of pumps and offers installation, maintenance, servicing and advice. As an Emotron partner, Pumphuset offers total solutions that include Emotron shaft power monitors, softstarters and variable speed drives.
The collaboration between Peter Johannisson, an installer for Pumphuset, and Franc Rostedt, an operations engineer at Sollentuna Energi, goes back about five years.
“We’re very satisfied with Pumphuset,” says Franc Rostedt. “Their good service and high competence are very reassuring. Working with a local supplier is also a huge advantage as if any problems crop up they can be on site very quickly.”
Boosting water pressure
There are two booster stations in the Sollentuna district heating network. One of them is in the part of town known as Häggvik. When this station was rebuilt in connection with road works, Sollentuna Energi took the opportunity to upgrade the pump control system at the same time. It turned to Pumphuset, who chose the new Emotron FDU 2.0 variable speed drives. The drives were brought into commission in the spring of 2006 and acted as a pilot project ahead of the product launch that autumn.
The pump station has two Emotron FDU units, the first 75kW and the second 90kW. They control two pumps that are run alternately a week at a time. A third pump with a separate control system acts as a back up. Operation is demand-driven and controlled on the basis of the difference in pressure between the water distributed to the subscribers and the water that returns. The difference is measured in substations along the network where sensors send signals to a pump computer. This in turn tells the variable speed drives the pumps' reference values and actual values.
“We’re seeing lots of benefits with the new Emotron FDU drives,” says Johannisson. “Installation is simpler and cheaper thanks to the smaller size and higher enclosure class. We now have two wall-suspended IP54 units that cope well with the heat. During the spring and summer months the temperature can get up to 35–40°C in here. And that places huge demands on the equipment.”
Another new feature that Johannisson and Rostedt can see being extremely useful is the I/O card that allows an EmotronFDU2.0 to control up to seven pumps without a PLC or other external equipment. They are also going to make use of the built-in shaft power monitor to protect the pumps..
The EmotronFDU2.0 also has several new features that make it even more user-friendly. Johannisson and Rostedt say that the most important thing is the option to select which process unit, for example flow, is shown on the control panel display.
Another advantage is that the control panel is removable and has its own memory.
“This allows us to download the program we’ve created and copy or move it to the other Emotron FDU units. The facility to connect a PC cable directly beneath the control panel on the front also means that we don't need converters anymore.”
Process optimisation
EmotronFDU2.0 variable speed drive optimises the operation of pumps, fans, compressors and blowers. Processes are protected from damage and downtime, with benefits from reduced installation, energy and maintenance costs.
Soft starts and stops protect equipment. Reduced start currents result in smaller fuses, cables and energy bills. Controlled stops eliminate the risk of water hammer and other costly damage. A built-in shaft power monitor and a novel Load Curve Protection function protect processes by immediately detecting any situation that could cause inefficiency or damage. Early warnings and safety stops allow preventive action. It also regulates flow and pressure by continuously adapting motor speed. This reduces energy wastage and unnecessary equipment wear. A sleep function further reduces energy consumption by pausing the motor when it is not needed.
An automatic pump rinsing function increases efficiency. The pump is set to run at full speed with certain intervals or a certain time at start-up to rinse out sludge. Multiple pump or compressor control is a reliable and cost-efficient method of keeping a constant flow or pressure despite varying demands. Emotron FDU controls up to seven drives.
Operation parameters can be set in a user's own process units – m3/min, bar, Pascal – making monitoring easier and more reliable. The removable control panel has a copy function for transferring settings to other FDU units. The virtual connection of logical functions, comparators and timers means no cables or external I/Os are required.