Heating Water Backflow Devices in isolated locations for livestock tanks

coh20operator

I was tasked with an interesting problem.  We have livestock tanks run by our water district that are in incredibly isolated locations.  These water tanks fill from the bottom and are made of concrete.  Replacing or modifying these tanks to comply with new state regulations pertaining to backflow and cross connection control would be extremely cost prohibitive. And the same would apply in running electricity to these sites.  The backflow devices required for both the hazard level of the tanks as well as the applications (back pressure and back siphonage) would require a preventer that has to be installed above ground.  We do insulate these devices and the lines feeding them with insulated boxes that provide a decent amount of protection from the wind and the cold, and everything will also have insulation directly applied to them.  The problem I keep running into is the heat tape that we currently use to keep these from freezing draws quite a bit of power, and runs on AC.  And as far as I know, the systems that would be able to provide the necessary power would be both large, and expensive.  I am looking for a way to keep costs down as low as possible while also installing a system that doesn't require extensive maintenance.  Does anyone have any idea what kind of output I would need to keep these in between 40 and 50 deg F constantly, day and night, wont drain a battery down to zero in the middle of the night and allow these rather expensive devices to freeze?   Any ideas would be seriously, seriously appreciated.

NANOcontrol

I heat water with PV solar without batteries. Storage will always be a problem with batteries. Storing heat in an isolated water tank would be one way to overcome the need for batteries. Pipes and equipment could be heated with PV electric in the daytime and stored hot water could be used overnight to maintain temps. It is a rather simple idea, but where are you going to find someone to implement it. Cycling water thru the equipment without heating is another thing which might be added to the mix. If you were close by it would be a fun control system. Keeping it to standard off the shelf products would be difficult as well as finding someone to maintain it long term.

coh20operator

I definitely thought about circulating heated water through the system to keep things thawed, but with limited space inside of the box that the device is in, the tank would be too small.  The locations that these are going to be placed are out in the open, and miles away from anything.  Wind definitely has to be taken into account as it is always blowing out here since there aren't many trees.  The heat tape (pipe trace tape) runs on 120v and pulls ~6w/ft. The standard length is 12' so the tape draws 72w upon operation.  Usually, if the tape is operating correctly, it should only turn on at about 37-38F and turn off at 50. So it likely, would not run all day, and would mainly be running at night.  If we stay with the type of tape that we usually use for these backflow devices, an inverter would certainly be needed.  I just don't know enough about solar systems to know where to start as far as how many watts would I need from the panel? what kind of battery (if needed) would be best to use, and i'm assuming that there would be some power loss through an inverter as well.  A lot of considerations for something that I'm just not familiar enough with.  

mcgivor

Some time ago I was involved with a pair of back flow prevention valves installed in a concrete enclosure at the street of a school , one was for domestic water, the other for the fire suppression system. Both were insulated without any auxillary heating, about 5 years after installation there was a period of 3 weeks at -40°C /-40°F during Christmas break, the valve for the fire system froze splitting it.

My role was to provide heat tracing and monitoring to prevent a future event. To establish a baseline I installed a temperature logging device to both to understand when auxillary heating would be required. What I discovered was the domestic side never got close to freezing, probably due to water moment provided by auto flush urinals, the sprinkler one was significantly colder due to stagnation. Ultimately it was decided to heat trace both as auto flush was being phased out in favor of proximity flush valves.

The amount of heating needed if well insulated is supprisinglying small to maintain a temperature ~5° above freezing  as long as there  is no wind, the heat trace cycled on randomly as required.

Creating flow my be all that is required, obviously having some source of auxillary heating would be better. Solar heating during the day would greatly reduce the risk of freezing as it takes extremely long for the valve to near freezing, again if insulated and free of wind.

Heat trace will work with DC as it's a resistive load so an inverter isn't required, the voltage will have to be near to 120V to achieve the same heating performance, solar panels can be series wired to achieve this. Perhaps 5 ×100W panels in series connected directly to the heat trace without any other devices would work but that is merely a theory, some experimentation would be needed and doesn't account for snow covered panels. 

icarus

How far away from the tank CAN the back flow protection be?  Would it be possible to install the back flow device(s) at the beginning of the lines where they branch from the service main(s) and might that put you closer to grid power?  

Heatline of Canada makes a good in the pipe heat tape, configured to run on 12 vdc.  Semi conductor so that it only heats as needed.       A well insulated box above grade, with insulated piping with in the pipe heat tape might only draw a few amp hours.      A day when cold enough to be needed.  Also, if you insulate the  devices  and protect them from the wind, is it possible the  normal flow through the water line be enough to keep them from freezing.  Keep a dribble going 24/7 in cold weather, will go a long way preventing a freeze.

tony

NANOcontrol

Could you provide a picture of this? It sounds like you want this to happen but unwilling to make any great modifications. As said before you can heat in the day and release over night with something that stores heat. Something as simple as embedding heating elements in some concrete will do that. Grid tie panels are super cheap and work well with 2,000W 120V heater elements at 60V. sticking that in a block of concrete would be simple.  If you drop the voltage in half of a standard heater, the power drops to 1/4 of the rating.

coh20operator

DC heat tape would be ideal as inverters alone are sure to use some of the power just on their own.  The "hotbox" as we call it is an insulated stainless steel box that is anchored to a concrete pad.  Insulation wise these are almost enough on their own to keep the RP's from freezing, but heat tape is always preferred just to make sure that these expensive devices don't freeze.  The box will likely be installed 5 to 10' from the water meter and it will be closer to the meter than the tank to make sure cattle don't rub on it and knock it over.  It's not going to be very far from the meter, and therefore, not very far from the main line, unfortunately, the main servicing these particular meters is a dead end line with one of the meters actually being on the end and miles away from the water source.  So the water temperature during the cold months can get as low as 35 degrees.  Initially, I figured that insulating the device inside the box would almost be enough to keep it thawed if the water was flowing enough.  I'm not an expert on cattle by any means but I wouldn't imagine that they would be drinking from the tank much at night.  But when they do, they're on a float system so if there are enough cattle drinking, the water should be moving from a good part of the day keeping things warm enough.  I know that insulation alone would be able to keep these from freezing for a good part of the winter.  But as unpredictable as weather can be here, it can, has, and likely will, drop well below zero both with and without wind.  So, I would imagine that some maintenance would be inevitable, such as clearing snow, and dust off of the panels, but the less electronic workings that have to be in place to keep heat on these, the better.  So a DC powered heat tape would be ideal, but we do use an AC heat tape on these when there is power and they only use 72w for a 12' length of heat tape.  Would it be worth it at this point to use an inverter and run that tape? Or would a DC system be better?

LucMan

Removing the water is always better than trying to keep it from freezing.
Adding a dip tube from the bottom feed of the tank to the top of the tank even with the water level would solve your problem of back pressure and back siphon. Then installing a 12v DC solenoid valve below the frost level  draining to atmosphere when temps are below freezing would allow the piping to drain. A single panel, battery, solenoid and Tstat should do the trick.