Modified Blower Operation

[pdab09]

Hope I've not got the wrong forum for this....

My neighbours and I have to share a private sewerage plant as we’re off the beaten track. The plant had a 0.5HP single phase blower which oxygenated the treatment plant. The blower ran 24 x 7. That said, when it broke down the maintenance company didn’t seem too concerned that it was out of action for more than 3 weeks – “It’ll be OK – it’ll catch up once replaced” they said. Eventually they put a 0.75HP replacement blower in (the blower output was bigger hence the bigger motor) and they said that it would be better on the basis of a more powerful blower presents more oxygen to the plant and this leads to a better bacteriological treatment. (I totally accept their reasoning and the fact that they couldn’t replace like for like – I know the manufacturer ceased production of the smaller blower some years ago.)

Anyway, it’s proving a little expensive to run and in order to cut our running costs down (and do our bit to save the environment!) I’ve a few ideas which the contracted plant maintainer doesn’t seem too keen on. These are as follows:

1. Use a programmable, solid state ‘Cyclic Timer’ to control the blower motor – 1 hour on followed by 1 hour off – cycling round again and again during peak hours but run it constantly during off peak (e.g. typically 11PM through to 6AM – this for ‘catch up’ purposes). With that I would save 35% of my blower running costs. Anyone any thoughts on my plan and experience of a suitable cyclic timer? My plan would also cut down a little on consumable parts i.e. blower air-filter (negligible cost) and the blowers carbon vanes (~£160 every 6 months).
   
   
2. Use a simple solid state timer to control the blower motor. Leave it running constantly for 17 hours peak time but turn it off via the timer for the 7 hours off peak. This would save me approximately 31% energy costs plus a proportional amount on consumables. This solution would be somewhat easier as a relatively cheap time would do the trick.
   
   
3. Using a Cyclic-Timer again programme it to run 1 hour on / 1 hour off round the clock - this would save a full 50% on energy costs.

I’ve run this by our maintainer who shook his head and advised against it. I can’t help feeling he just sees it as an added complication and it’s much easier for him to say ‘No - run it constantly’. I should point out that maintenance includes carrying out some rudimentary tests on the treated output. If with implementing one of my plans the quality of effluent fell I would simply modify the timer(s) to give the blower more run time or set it to constant. With that we’d be a little out of pocket but back to square one. Also, I’ve not got an ‘Off Peak’ energy account yet but trust I could get one. Off peak times seem to vary from supplier to supplier but they all seem late evening to early morning. I should point out that any work would be contracted to a bona-fide electrical contractor.

Anyone any experience or any thoughts on my suggestions? All inputs appreciated.

 

[westward10]

How is it currently switched on and off.

 

[pdab09]

How is it currently switched on and off.

It's effectively via a main, rotary switch (and I'm guessing a contactor). As long as there's power to the plant the blower runs as the plant is constantly on by design for other control purposes - emergency alarms, solenoids, fluid pump, etc.

 

[Spoon]

I would ask the maintenance company, if it's ok for the motor not to run while it it faulty for 3 weeks then why is it not acceptable for the motor to run just in the 'off peak' period.
You need more info from them than ‘No - run it constantly’.

 

[Lucien Nunes]

If the motor has a start-relay, PTC thermistor or centrifugal switch (the latter unlikely these days) then as well as a total run-time life limit, it also has a maximum number of start cycles before one of these parts breaks, and that does sometimes kill the motor too. So they might have had bad experiences with too-frequent starting. This does not apply to permanent split capacitor motors though, which have no starting aids to wear out.

 

[pdab09]

If the motor has a start-relay, PTC thermistor or centrifugal switch (the latter unlikely these days) then as well as a total run-time life limit, it also has a maximum number of start cycles before one of these parts breaks, and that does sometimes kill the motor too. So they might have had bad experiences with too-frequent starting. This does not apply to permanent split capacitor motors though, which have no starting aids to wear out.

Thanks Lucien. The blower is just 6 months old. Quite certain it doesn't have any starting aids. That said your comment makes me think that should I go for one of my intended solutions I may fire off an email to the Elmo Rietschle support team - I don't want to invalidate warranty!