Variable sped drive for a pump motor in a shower

[schnell]

Hi,

Do you have any suggestions for a motor and a variable speed drive combination for a pump for a domestic shower?

We already have a fixed speed AC motor as a pump, but now we want to do variable speed drive.
(so people can have variable pressure shower water, as they choose)
Our fixed speed motor has a fan, so we cannot use this motor with a variable speed set-up, as the fan would spin too slowly at the lower pumping settings.

We also want to do it cheaply, so am i right in saying that we are looking at a thyristor drive?

We are thinking of say a 3-speed drive, or in fact we may consider a more widely variable speed drive, if its not too expensive.

I believe Triac drives are out becuase of the non-symetric nature of triacs.(?)

 

[NGLENGR]

I think Grundfos is big in the residential and commercial water supply/distribution systems. They have pumps with integrated motor/VFD packages that might be a better solution for what you're wanting.

 

[jonr12]

You will not be able to speed up the pump using a VFD. So if the pump is not large enough for the shower now, you need a larger pump. Then variable pressure for the shower would only require a pressure reducing valve.

 

[schnell]

The problem with using a large pump and pressure reducing valve is that it wastes energy, as you are creating all that high pressure with the pump and then stifling it with the flow reduction valve.

-the energy regulatory bodies are after us and we need an efficient flow control of shower water, and thus we are looking for a variable speed drive for the pump.

 

[waross]

How big is the shower and how much energy will you lose, in dollars?
Remember that the energy loss is in the form of heat, and if your reduction valve is causing losses the losses will slightly warm the water meaning that less water heating is needed.
You should compare the cost of electrically produced BTUs (valve losses) with the cost of water heating BTUs (gas, oil, electric, solar) to evaluate your real world losses.
If your water is electrically heated there may be no net loss of energy when a reducing valve is used.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[schnell]

the hot water is already pre-heated in the boiler.

we have a hot and cold tap mixer so the customer gets their desired temperature.

Its just your normal type of domestic shower, except with a flow rate from really nice and powerful , to less so.

 

[potteryshard]

As I envision your pumping arrangement, you have a booster pump (assumed to be centrifugal) in line with the shower head, and are looking for an adjustable boost pressure above the incoming line pressure.

It doesn't sound like you need a feedback loop or inherent pressure regulation; just an adjustable boost above baseline.

It seems to me that a series AC brush motor (think of an electric drill motor) might be the least costly and most effective way to accomplish this. The AC brush motor can be controlled by a simple voltage chopper (think of the trigger on your variable speed drill) and is inherently a varying speed motor which would seem to want to develop a relatively constant torque above the float speed (as determined by the baseline flow) of the impeller.

Cumulative run times would not seem to be overly large so that brush life should not be an issue. Above all, AC series brush motors (and controllers) can be very inexpensive, ase well as having what seems to be desireable characteristics for you application.

 

[LionelHutz]

The problem with using a large pump and pressure reducing valve is that it wastes energy, as you are creating all that high pressure with the pump and then stifling it with the flow reduction valve.

Did you decide that must be the case due to all the stupid energy guides out there pushing VFD's as automatic energy savers? Do you actually have any clue as to the energy wasted or is that just an uninformed guess?

Your posts have make it very clear you don't have a clue about this stuff. Try at least posting the voltage available and required power rating and speed for this motor as well as the motor frame required, the very minimum that you should already know is required if you want a motor recommendation.

 

[jonr12]

All energy regulatory bodies need to learn how to read a pump curve. As LionelHutz said, “energy savings guides showing VFD’s as automatic energy savers are “stupid””, and so are the people who believe them. And a pressure-reducing valve is not going to add any detectable heat to the water, or have any appreciable energy loss compared to a VFD.

“Its just your normal type of domestic shower, except with a flow rate from really nice and powerful , to less so.”

I think this means you have a pressure switch controlling the pump. It will go from “nice and powerful” to “less so” as the pump starts and stops. I think this also means your pump is plenty large enough for the shower. You just need a way to keep the pump running and the pressure steady. Backpressure or reduced flow from a pump control valve will do this, and also reduces the energy consumption of the pump very similar to a VFD. A pump control valve will also work with a single phase motor, which you will have to change to a three phase motor to work with a VFD.

All this has been discussed many times. Maybe you should search for some old threads on the subject like this one.

http://www.eng-tips.com/viewthread.cfm?qid=260203

 

[waross]

The problem with using a large pump and pressure reducing valve is that it wastes energy, as you are creating all that high pressure with the pump and then stifling it with the flow reduction valve.

Where do you think that the wasted energy goes? It probably goes into the water so that the customer uses a little less pre-heated water from the boiler and a little more cold water to get the desired temperature. It is really hard to waste energy when you are mixing hot and cold water to achieve a water temperature less than the maximum temperature of the hot water.

The last time I had hands on experience with a shower problem it was a real gong show;
One expert wanted to throw out the supply pump and install a larger pump.
Another expert wanted to dig up the piping between the supply pump and the house and increase the size.
There were two shower heads and numerous body wash nozzles. the water only made it to the lower two levels of body wash nozzles. The upper nozzles and the shower heads were dry. With the shower mis-performing at maximum there was still sufficient water available at the wash basin.
The solution:
Replace the energy efficient flow limiting control valve that would barely pass enough water for one shower head with TWO commercial high flow shower control valves.
I have no doubt that you have problems but your guesses and assumptions leave me wondering if you will find the source of the problem before guessing at more solutions.
There are many inline booster pumps available for domestic service. There are shower valves available that will both mix and control the flow. No electronics needed.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[schnell]

Hello,

My Boss would love it if we could get away from electronics.....but we have lots of it!

We wish to use variable speed drive because if we use a valve to staunch the flow, then we cannot get down to 11 litres per minute without getting cavitation problems which causes far too much audible noise.

-therefore we need to use a variable speed drive……and I wondered if the below schematic was looking good…its just a single Triac.



Our current pump is brushed, AC driven (230V / Single Phase / 50 Hz) and, as such, is fixed speed with constant pressure output….but we will drive it with our variable speed circuit (below)

So, -We wish to make it variable speed drive

Here are the details of the pump we use currently, at fixed speed:-

Power = 405 Watts, 33 litres/min

Detailed datasheet of pump = Part No 46407

http://www.stuart-turner.co.uk/media/13214-Showermate-Standard-Twin-Datasheet.pdf

General data on this Pump = Part No 46407

http://www.stuart-turner.co.uk/products/showermate/s18-bar-twin

Here is the schematic of the Variable speed driver circuit proposed:
(-just a triac triggered by a microcontroller via an opto…..the microcontroller knows where the zero crossing of the mains is)

http://i52.tinypic.com/23u2xxu.jpg

 

[davidbeach]

Single phase motors and VFD don't play well together. You will need a 3-phase motor. At those sizes you can get a VFD that will work with only two of the phases connected.

 

[waross]

Our current pump is brushed, AC driven (230V / Single Phase / 50 Hz) and, as such, is fixed speed with constant pressure output....but we will drive it with our variable speed circuit (below)

Motor Type, Induction, Permanent Capacitor,
Auto Resetting Protective Thermotrip

??? PSC motors don't have brushes.

We wish to use variable speed drive because if we use a valve to staunch the flow, then we cannot get down to 11 litres per minute without getting cavitation problems which causes far too much audible noise.

This would make the twin shower version of the pump unusable with only one shower.
The problem seems to have changed from "Too much losses" to "Too much noise".
Whatever it takes to justify your desire to build a circuit that won't work with the motor that you intend to use.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

How did you come to the conclusion an induction motor is "brushed"?

That circuit is useless for this application. You need to vary both the voltage and frequency to speed control an induction motor.

 

[jonr12]

That motor shows to come only in single phase. As Davidbeach says, you need a three phase motor to work with a VFD. And as LionelHutz says, you will need a VFD to vary the voltage and frequency to control the speed. I think the VFD will make more noise than restricting the flow with a valve. In my experience pumps seem to run more quite when the flow is restricted. You could test this by simply installing a ball valve on the discharge of the pump. Have someone manually control the ball valve to maintain a steady pressure in the shower. If it works as I believe it will, then a good control valve will be even more quite than the ball valve.

 

[schnell]

Hi

I have the motor on my bench here now....i can gaurantee it is brushed, as i can see them.
-i think the supplier just calls it a fixed speed, AC motor, rather than an induction motor.

My naive circuit is bad i now know.

This motor is to 400W and a full power factor correcting boost converter , followed by a Variable speed drive, probably a h bridge would be needed, as you have said.

 

[RobWard]

Is this for a product that you wish to sell on a commercial basis?

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[schnell]

-sorry about this.

That motor above is one of ours but its not the one for which we will be having the VSD.

The one that needs the VSD does not have any ID on it, other than on the enclosure which says "220-230V ,250W, 50Hz IPX4".

It has brushes.

on the laminations is marked

"645064
230/50
01405"

sorry about this,

my initial job here was just to make the SMPS....but the VSD has just been thrown in aswell, and the people who chose this motor etc have now left the company.

 

[davidbeach]

Possibly a universal motor where speed is proportional to voltage and frequency has nothing to do with it. There are various types of speed controls for various type of single phase motors, but you won't find a VFD any where on the matrix.

 

[BrianE22]

Brushed AC motor? Possibly it's a universal motor. Can you take it apart and post pictures?