hot water flow sensor

[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

[Darrel Taylor]

Looks like it's safe to post again. Yahoo!

>> What kind of water capacity does your commercial unit hold?

I have an under sink model, which looks like it could hold maybe a half-gallon. Yours sounds bigger.

It might be tricky getting a fast enough response from the temp sensor. The tube and epoxy might slow things down with the extra mass. But ya gotta isolate it somehow I guess.

... mechanical back-up ... good idea.

Can't wait to see what happens.

DT

[SteveB]

Hey Jessy,
Here is a link to the Tankless system I've been using for the last year: http://www.seisco.com/pages/internal-dia4.html. May help with the conceptual ideas. Of note, notice there are individual cambers for each heating element. Allow for future easy replacement of the heating elements, as this is the most likely component that will require replacement. Can't really speak to the corrosion issue (The one I have is actually made out of a non metal polymer). If you have hard water, you sould allow for easy cleaning out of the cambers to get rid out the scale build up. Also keep in mind, these can draw a lot of current. So make sure your electric service to your house is up to the task. The sight above has some good info on that as well. If you look around a bit on the web, you may find some temp probe products that would work well. If you construct your own, here is an epoxy designed for heat transfer that would work well.

As for using the solar heater as a preheater, you need to "protect" the backup heater (and people) from the excessive temps possible from a solar system. Simply put, use a passive temperature controlled mixing valve between the solar water heater and the backup water heater. This will allow water temp into the backup heater to be at, or below, a preset temp, which would be 5-10 degrees above the max output temp of the backup heater. This way, the backup heater only comes on when the solar has run out. And the hot water from solar water heater, when it is really hot, will be used at a slower rate, increasing its effeciency.

Darrel:

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.

I've seen some set-ups for between $1000-1500 (here's one). With this setup (where I live) I could probably recovery my costs in three years. Even if the thing only lasts 10 years (likely more), I am money ahead, especially if energy costs continue to climb. I am actually planning to go this route in the fall (at the same time my roof is replaced). We have so many good solar heating days here that I my not really need a backup heater for 10-11 months out of the year.

Good luck jessy. Keep us updated on how things work out.

Steve


BTW, if you would like a closer look at one of these let me know. I could take some close-up pics.

[jessey]

Hi Darrel & SteveB,

Thanks for all the info and the links. I'm now waiting for a friend to return my plasma cutter and as soon as I get it back I'll be starting my project. I think I'll use a copper tubing (for better thermal conductivity) for the DS1820. I enquired to the link that you sent me SteveB for a good thermo substance, I described my application and just got an email back today suggesting to use Artic Silver Adhesive and also got a phone number for arctic silver so I'll call them tomorrow to see what they have to say.

Could anyone here suggest an alternative heat transfer compound (maybe not the best but something that will work to try) that is widely available and easy to get just in case I have to wait for the artic silver adhesive as I live in Canada and sometimes I have to wait a few weeks for some stuff to clear customs. If Active Electronics carry it then I shouldn't have to wait too long.

Its hard to tell in a lot of the pictures of the electric on demand water heaters in the sites that I visited but I would assume that the enclosures for the heater elements are round with convex ends (like a hot water holding tank) so I think my flat design will have to be beefed up somewhat to withstand the extra stresses especially if the water pressure is high. A friend suggested drilling multiple holes in between the length of the elements and using solid round stalk inserted into the holes and welded on each side of the tank to beef it up, a good idea that I think I'll employ. What is the shape of your tank for the heating elements Darrel? Looking at the pictorial drawing of SteveB's non metal polymer tanks, it looks like they are round as well which I think results in less psi stresses overall.

I think I'll put the solar thing on hold and just try and get the heaters working with the code that I posted for now then if I get it working good then I'll consider it. Green is good.

Anyways, thanks for your help and I'll keep you informed on my progress, maybe with some pictures later on.

Thanks
jessey

[Darrel Taylor]

Round here too.

Here's a model that's similar, except ours has a relay, instead of triac.
http://eemax.com/operations%20manual...SP%20instr.ppt

Like I said, it's small.

DT

[air1kdf]

Cool project.

DIY solar setups can be very inexpensive, check out ebay.

I am setting up a solar panel system to heat my 30,000 gallon pool. There are systems like Goldline that make and sell differential temp systems to optimize the heating. They also use 10k thermisistors that sense temperature. There are many sensors that can be placed inside or outside of your setup.

If it was me, I would use 2 sensors. 1 going in, 1 going out. Make sure to add code for circuit failure(like no temp reading, and invalid readings).

I would also forget about limiting flow. It would prove to be more complex than it needs to be, expensive for the control valve and actuator, and a PITA for the end user.

The thermal grease that you mentioned is great for putting a fan on a CPU. But it is a grease and not an epoxy.

FYI a 4x10 ft panel made 20 years ago can boil water in 5 minutes.

[BobP]

Hi,

This may be a simple and cheap solution. When I installed my power shower I was surprised to notice that the flow sensor on the outlets of the pump were no more than a magnet and reed switch positioned on opposite sides of each of the 2 plastic outlet pipes.
I can only assume as the water flow starts the magnetic field changes releasing the reed switch.

It is simple and cheap enough to try?

It has worked faultlessly on the pump for over 2 years now.

Hope this helps,
BobP

[Ken Howell]

It might be tricky getting a fast enough response from the temp sensor. The tube and epoxy might slow things down with the extra mass. But ya gotta isolate it somehow I guess.


DT

I've put these temperature sensors in small copper tubes (about 3/16...just big enough to encompass the housing) and epoxied them for environmental sealing.....they seem to respond almost instantly to increased temperature from holding them between fingers.....so I don't think the lag on temperature measurement is going to be a problem. You will have to have one hell of a heater unit to match temperature rise with water flow. This is especially true if your water temperature changes with the seasons as ours does here in Boise, Idaho.....