Occasionally we have a client managing a site with a fixed speed cold water booster set where they're experiencing fluctuating water pressures. It can be a frustrating issue to deal with, as inevitably when an engineer goes to investigate it seems to be working fine.
It's not only service problems it causes, either. Additional load on the pipework and on the pumps can reduce the lifespan of the system, and it will be energy inefficient too. So you can add high additional costs to the service problems you're already hearing about. There's four common solutions to this problem that we work with.
The first and the best solution is to fit variable speed drives to the booster set. There's lots of benefits here:
1. Reduced energy cost, as pumps only run at the minimum required speed.
2. Reduced stress on pipework caused by water hammer.
3. Increased pump motor life, as the inverters have a soft start/stop function and the pump only runs as required.
4. The perfect pressure water supply, with adjustable pressure set points.
5. Consistent supply, with auto changeover of duty in the event of pump failure.
6. Even pump wear, by automatically balancing operational hours across all pumps.
7. Improved functionality (if they are integrated with a BMS or monitoring system).
NB: the above picture uses on-board inverters, but there's advantages to be had by using off-board inverters instead - contact us for details.
It sounds a bit simplistic, but it's a fact that increasing the size of the pumps will reduce fluctuations in water pressure. This is because several smaller pumps trying to cope with a varying demand will be starting and stopping more often, whereas larger pumps will cope with a small change in demand without any noticeable changes in the output from the pump.
Pressure regulating valve
A simple and effective solution is to fit a pressure regulating valve on the discharge from the booster set. These are set to a specific pressure, and if the output from the pumps goes above the set pressure then the valve still maintains the set pressure beyond the booster set. They can also be installed for each part of the system, for example in a block of flats: installing one at the branch off to each flat ensures consistent water pressure throughout the block.
If the booster set doesn't already have a jockey pump, this is a good way to combat fluctuating water pressure (particularly in combination with installing bigger pumps). A jockey pump takes up the slack between each pump. When one of the pumps can't quite keep up with the demand, the jockey pump provides the small amount extra needed instead of starting up the next pump on the set with a considerably higher output.
As always with this kind of advice, it goes without saying that not every solution is best suited for every system. In our experience these are the most common fixes that are required, so it could be that they help you too. Either way, get in touch with us to discuss our solutions to pump-related challenges.