hot water flow sensor

[Dave]

jessey, Use an inexpensive diferential pressure transducer across a fixed orifice. There are many different company's out there that supply small diferential pressure transducers. Motorola MPX2100 first comes to mind but there are many more... LOL

Dave Purola,
N8NTA,

[Darrel Taylor]

Jessey,

If you can accurately control the temperature of the water, then you don't need a flow sensor. Just maintain the water at a slightly elevated temperature, under no flow conditions. Once the tap is turned on, the water temperature will suddenly decrease. Detect the change to turn on the heaters. When the tap is closed the heaters will turn off, due to normal temp control. If they are off for a certain amount of time, revert to standby mode, which allows it to slowly cool off again.

That seems to be how our's work. It has a relay that clicks on for about 10-15 seconds every 20-30 minutes, just to keep it warmed up.

.

[jessey]

Hi Darrel,

That sounds really good as it would certainly make it more affordable and simpler to build. I'm not sure if I'd really need it but what do you think of having the micro control a Proportioning Valve on the inlet side of the heating unit which could control the amount of water passing through the heaters so that if I use a solar pre-heater for the in coming water supply then the incoming water temperature could control the flow rate. The warmer the incoming water then the more flow rate I could have and when the incoming water temperature was cold then the micro could limit the flow rate some if needed to maintain a minimum preset output temperature for the water? Something to think about.

I managed to fix my hot water tank yesterday with an epoxy glue for now so I won't be rushed to get this done and can now take my time. It sure is nice to have hot water again!

I was thinking of just welding a rectangular box together just big enough to house the heating elements with an inlet and outlet for the water and of course a pressure relief valve and possibly a sacrificial anode for corrosion protection. I'll do a search for some kind of anti rust protective coating for the box but that can be later. Thanks to all for the comments about doing this.

Thanks
jessey

[Darrel Taylor]

Personaly, I think I would rather sacrifice temperature, than flow. And the main heater will take up the slack if it's not hot enough anyway. The Solar Pre-heater is there to save money, which it will do by not making the main heater work so hard, but the end result should be the same... Full-Flow, hot water.

I never really understood the Solar Idea too well. You end up spending Thousands of dollars, just to save a few hundred bucks in electricity. Kind of like buying one of those Hybrid cars. Pay an extra $10,000 to save $500 a year in gas. Doesn't add up.

If you can, use 316 or at least 304 stainless steel for your box. 316 will last forever, 304 will still rust a little, but it's cheaper. If you have Hard Water, it will soon be coated with calcium which helps with the corrosion too.

However if you use the anode ... I hear that sacrificial Zinc's can help prevent Cold's.

.

[Ioannis]

... If you have Hard Water, it will soon be coated with calcium which helps with the corrosion too.

However if you use the anode ... I hear that sacrificial Zinc's can help prevent Cold's.

.

How about Water Descalers using Electic Field? Has anyone used them? What were the results?

Ioannis

[jessey]

Hi Darrel,

Thanks for all your suggestions and for giving me an approach to follow for doing this. Well I finally got my test code working good, at least on the bench for now anyways. I thought I'd post it for you and others to have a look at for any possible comments. Once I build the unit to see how it works then I can cut the size of the program down considerably.

It's a fairly short program. I have (probably not needed but good for testing) created variables where as I can programme the temperature of the water coming out of the tap, an adjustable high limit temperature point for safety and also to know when the tap is off. And instead of a timer in the program & relay to control the ambient temperature when the tap is off I'll have it temperature controlled. I'm also thinking that I should have a differential for the ambient temperature of a few degrees so the relay or triac (relay for now) doesn't chatter or cycle too often.

I'm just going to use mild steel for the prototype to see how it works then when I have a good design then I'll switch to stainless steel construction. My first design will be a unit just big enough to house the heating elements with a very minimum water capacity. What kind of water capacity does your commercial unit hold?

For the DS1820 sensor, I was thinking of getting a suitable sized stainless steel tubing and epoxy the sensor into it then with the appropriate size fitting installed into the tank use a furrow and a nut to secure it into the tank or just epoxy the sensor to the outside of the tank. Any suggestions for accomplishing this?

Thanks for your help and I look forward to any further comments that you or anyone else here might have.

Thanks
jessey

[jessey]

Hi Darrel,

The code I posted in the last post is not correct, I caught it after I posted it. The new revised code here has been tested and is working good.

I'm now thinking of putting the DS1820 on the bottom of the inside of the tank directly in the path of the incoming cold water (epoxyed into a SS tube) so my code will catch the sudden temperature change.

I was also thinking of placing a mechanical reset-able high temperature limit switch on the side of the tank for added insurance. I can use the same one that was on my old hot water tank.

Thanks
jessey