Anti-Freeze Question

[Bee Keeper]

Currently I'm planning to construct a small green house (12'x16'x8') and wanted to heat the green house using evacuated tubes. The heated water would be stored in a simple insulated (home built) tank and the heated water would be circulated to PEX tubing placed in the concrete floor when needed. Living in northern Idaho will require that the tank be fairly large to support the thermal losses in the green house under worse case conditions. A back-up propane hot water heater would be used in emergencies. The heated water would be circulated via 3, small 12 volt hot water pumps.

To my surprise (and concern) is the cost of anti-freeze for this type of system is huge. While it would be a closed loop system, it would still require a considerable amount of anti-freeze. In this case, the anti-freeze would need to be compatible with the PEX, Tank Lining, pump and propane hot water heater.

Having said all that ................ where best to start in researching and evaluating anti-freezes ? What options might I consider ?

Thanks in advance for the help and advice.

[inetdog]

Currently I'm planning to construct a small green house (12'x16'x8') and wanted to heat the green house using evacuated tubes. The heated water would be stored in a simple insulated (home built) tank and the heated water would be circulated to PEX tubing placed in the concrete floor when needed. Living in northern Idaho will require that the tank be fairly large to support the thermal losses in the green house under worse case conditions. A back-up propane hot water heater would be used in emergencies. The heated water would be circulated via 3, small 12 volt hot water pumps.

To my surprise (and concern) is the cost of anti-freeze for this type of system is huge. While it would be a closed loop system, it would still require a considerable amount of anti-freeze. In this case, the anti-freeze would need to be compatible with the PEX, Tank Lining, pump and propane hot water heater.

Having said all that ................ where best to start in researching and evaluating anti-freezes ? What options might I consider ?

Thanks in advance for the help and advice.

First look at the chemical composition. Some anti-freeze solutions are 100% glycol or have some small amounts of other chemicals to improve their stability, etc.
Some are designed for automotive use and are full of corrosion inhibitors and other chemicals to make them compatible with mixed copper, iron and aluminum systems.
Others are a mixture of glycol, alcohols, and other ingredients and are designed to keep the toilet bowl in an RV from freezing.

Some posters have indicated that by using the right choice of RV solution they get a better price per gallon than by going to a plumbing supply for (relatively) pure glycol.
YMMV.
Since your fluid loop and tank would not be one hole in a heat exchanger away from domestic hot water, you have a lot more freedom to choose, but you still need to make sure that what you use is compatible with the pipes, valves, seals and other fittings in the system. Glycol is time tested and well understood.

Make sure that any pressure relief or drain valve will not spill the solution where animals can get at it, as most solutions are poisonous when ingested.

[Naptown]

OK to add a bit to this.
use an extremely will insulated storage tank. Non pressurized. If you bury the tank there may be no need for a glycol solution at all. In many cases like this the tank is buried in the floor of the greenhouse. The colllector loop is set for a drain back situation. This solves the summertime overheating problems with glycol as the collectors when baking in the sun under stagnation conditions are not cooking the glycol and turning it into glop. Straight water will conduct more heat than a glycol solution so it will gather more heat. This will require three pumps. One pump to gather heat from the collectors. One pump to circulate the heat from the tank to the floor radiant and a third pump to run the back up heat and provide freeze protection.

As far as different types of glycol are concerned there are basically three that are used.
Ethelene glycol the major ingredient in automotive antifreeze. highly toxic and an attraction to animals due to it's sweet taste.
Propelene glycol. Comes in 2 or more varieties. the most expensive is food grade. (yes it is a food additive) Second is the stuff for RV systems which is not food grade but is non toxic. (Every thing is toxic in a large enough concentration)

[peakbagger]

From personal experience RV PEG mixes sold at most stores is designed to keep pipes from freezing in RVs, their concentration and "protection level" is set up to allow the glycol to gell but not freeze. Unfortunately most SHW systems need to be able to pump the liquid and gell doesnt pump very well with a typical centrifugal pump so in the wrong conditions you can have a tank of "jello" and a hot panel and no way to get heat from the panel to the tank. By the way I was unsuccessful in getting the blend percentage that the various RV vendors used. My system is an indirect system where the loop is full of glycol and the there is a coil of copper wrapped arund the storage tank (looks like a hot water heater with two connection on the side).

So the next step for me was to drain the system and use a strong mix of Ice Block which is 100%polyethene glycol with a much lower temp rating. I cant remeber the mix ratio but it was around 50%.This reduced the temp my system would pump, but somewhere around zero, my DC pump doesnt have enough head to overcome the viscosity of the fluid in the system leading to the same issue where the pump is running but no fluid is circulating. I expect if I had gone through the hassle of calculating the head loss in the loop at different temps taking into account viscosity of the fluid, I would probably end up with a backup pump for cold weather or possibly a positve displacement type pump instead of centrifugal. The backup pump wouldnt have to run very long, just enough to get the fluid circulating. I think the hard part on the calculation is that the panels are excellent radiators on a cold clear night and I expect that the glycol in the headers and risers are probably subcooling realtvie to the ambient temp.

In your case some manually switched heat tape might be the least hassle.

By the way I have good friend that has had a solar hot water system for 25 years and he still is on his original charge of ethylene glycol (the toxic stuff used in cars). He checks the pH every year and its still fine. His system uses a submerged coil for his DHW (no longer legal).

[inetdog]

By the way I was unsuccessful in getting the blend percentage that the various RV vendors used.

For a pre-mixed solution, even though the labeling will not give percentages, the Material Safety Data Sheet required for the product will contain that information and has to be publicly (but not necessarily easily) available.

[peakbagger]

Annoyingly MSDS sheets dont neccessarilly contain the concentrations of the constituents, it lists the ingredients usually over a threshold value (in the following 1%) but not the concentration.

http://www.shamrockchicago.com/MSDSPrestRVAf.html

It was part of my research previously

[inetdog]

Annoyingly MSDS sheets dont neccessarilly contain the concentrations of the constituents, it lists the ingredients usually over a threshold value (in the following 1%) but not the concentration.

http://www.shamrockchicago.com/MSDSPrestRVAf.html

It was part of my research previously

It does not give details, but at least it gives you a range, which is better than nothing:

SECTION 2: PRODUCT COMPONENTS

HAZARDOUS COMPONENTS CAS#      PERCENT        EXPOSURE LIMITS
Propylene Glycol     57-55-6   20-40          None Established

NON-HAZARDOUS INGREDIENTS >1%
Water 7732-18-5

So the only ingredients over 1% are Propylene Glycol and Water, and the Glycol is between 20% and 40%

Other manufacturers may choose to give more information voluntarily.

[Sunking]

So the only ingredients over 1% are Propylene Glycol and Water, and the Glycol is between 20% and 40%

That means the water is between 60 and 80%. You can buy 100% Glycol, then mix in as much or little water as needed. Most commercial chilled water cooling systems operate at 100% glycol.

[Naptown]

If you are in the us RE Michael sells what you want but it is not cheap

[rainworm]

oil

ok so what is wrong with using oil in the pipes instead? or better ethanol in water solution? Has anyone tested a few pipes with this in various temperatures?

[russ]

ok so what is wrong with using oil in the pipes instead? or better ethanol in water solution? Has anyone tested a few pipes with this in various temperatures?

Maybe you think the various suppliers don't think about anything different?

[peakbagger]

By the way wikipedia has some good info on glycol including why using 100% glycol is bad idea with regards to freezing point (70% glycol and 30% watert has a much lower freezing point than 100% glycol.

http://en.wikipedia.org/wiki/Ethylene_glycol

[LucMan]

Make it easy on yourself use Tyfocor or Dow Guard , it's formulated for extreme temperature solar systems.
In the 70's silicon heat transfer fluid was used at a great cost , today propylene glycol is the way to go.