Piwoslaw,

Thank you for posting this info.

I'm still learning how designing with PEX works, too.

But I can answer your question about PEX diameter.

PEX comes in many different diameters.

In the USA, (and Canada too I assume), the PEX OD sizes are:

• 3/8"
• 1/2"
• 5/8"
• 3/4"
• 1"

I would guess that in Europe (where PEX started) PEX would be made to even metric dimensions, and that the step sizes would be roughly equivalent to the list above

The following notes primarily apply to PEX radiant floors...

NOTE 1: The 5/8" size is made, but not often stocked. If a design requires it, it can be found. Also, PEX sizes can go mich larger than 1". I limited the list because most PEX residential heating jobs would not usually require it.


NOTE 2: Assuming equal pipe spacing, the diameter of PEX does affect the amount of heat given off per unit area, but less than one might think. I found an excellent article by John Siegenthaler, the guy who wrote the bible on radiant heating. Here's a chart of various diameter PEX schemes:


The article is the best of its kind, should be read in its entirety.

He also did an article called Depth Perception, which addressed the optimum depth of PEX tubing in a slab.

Regards,

-AC_Hacker

Following this thread with great interest. The super insulated passive solar addition(a winter zone core) to my retirement cabin will have a thermal mass hydronic floor for the first floor and basement(larger w/sand bed) as it's main heat storage so DIY hydronics is of interest to me(building will be 75% DIY, getting older). I have come across a couple of radiant dealers that sell DIY "kits". Still want enough knowledge of "how to" to understand/adapt system to my best needs. Also still researching best/economical way to charge mass(other than passive already planned) with minimal "sysytems". KISS. Backup demand should be very small. Lucky to be building from scratch and can design for radiant.

Hello Drake,

I'm getting very close to plunging into my first radiant floor project.

I'm trying to scheme up a relatively lightweight 'sandwich' which will be high-efficiency. From all I have read, lightweight and high-efficiency are mutually exclusive, where radiant floors are concerned.

Have you thought about how you will do your floors?

BTW, I stayed at a house with nice warm slab floors this past weekend, and it was very nice indeed. I now know that it is well worth the effort to go radiant. They used a Rinnai wall mount boiler (propane).


I was amazed at how small the heating plant was for such a large house.

Regards,

-AC_Hacker

polarity seems to be present in so many things. It's those darn laws of physics. I will be lucky that I can design from scratch and I will be putting hdro in shallow sand/bed slab in basement and in engineered slab first floor. I too have experienced radiant floor heat and It is my wife's dream come true(next to moving south) steady heat - no setbacks. I must say your heat pump exploration is greatly admired, followed and of great interest. I wish I could contribute more than hope that you continue.

Thank you so much for your comment.

If you really mean it about wanting to contrubute more, then get a brazing torch and the basic tools, then find a doner air conditioner, or de-humidifier, build your own homemade heat pump and make it work for your new purposes... Take loads of photos, ask loads of questions and tell us what you have learned.

Regards,

-AC_Hacker

I am a "modifier" by nature. I can seldom not resist modifying most anything to better fit my needs. But working correctly and safely with refrigerants is a bridge I need to see if I am able to cross. I believe I've already used eight of my nine lives on other project so I must be cautious.

I know how you feel, I felt the same way myself, more or less...

But if you drive a car, you are taking a much bigger risk than working with refrigerants.

-AC_Hacker

I am at this time still educating myself on the principles of closed liquid heating/cooling systems and am lucky enough to have found your work that has shown DIY possibilities exist. Am also making sure I understand as well as I can what you have done, how well it meets what I want to do and design from there. I would really like to have the the heat transfer directly into an insulated tank on the radiant side and am trying to find out if there is a proper exchanger to do that with refrigerents.

I'm curious do they connect the boiler directly to the radiant or do they use a storage tank that is heated by the boiler then circulated out. It just seems funny to heat water to 180 or so with a boiler and then pump it into pipes when you really want 90 or so degrees.

Well, if I'm understanding your quandry correctly, the heat pump I built, and then one I am building now are just a refrigeration compressor, a cap tube, and two brazed plate heat exchangers, hooked up in a circuit.

Regarding the heat exchangers, one is on the "source" side, which I usually call the ground loop side. This is where the heat comes from. It has water running through the odd-numbered channels, and refrigerant running through the even-numbered channels. Just before the refrigerant enters this exchanger, it emerges from the metering device, in my case this is a cap tube. When it emerges from the cap tube, it passes from a region of high pressure and enters a region of low pressure. In that region of low pressure, the refrigerant instantly changes from a liquid to a vapor and becomes very cold, much colder than the loop water that is circulating through this exchanger, so heat from the water migrates from the water to the refrigerant.

The other heat exchanger is on the "sink" side, this is the side where the useful heat is available. It also has water running through the odd-numbered channels, and refrigerant running through the even-numbered channels. The vapor that had picked up heat from the first HX (above) is routed through the compressor where it is squeezed to a point that is close to condensing, but the vapor is too hot to condense. This hot pressurized vapor is then routed through the second HX, which in your case has water from the PEX floor circulating through it. The PEX water is cooler than the hot compressed refrigerant vapor, so heat migrates from the vapor to the PEX water. As the heat from the vapor begins to migrate into the water the vapor cools enough so that condensation happens inside the heat exchanger. This condensation releases very large amounts of heat which also migrates into the PEX water.


So, getting back to your original question, "...trying to find out if there is a proper exchanger to do that with refrigerents...", the answer is yes, there are many kinds of heat exchangers that can be used, but the best because of efficiency and also small size are brazed plate heat exchangers. They are usually too expensive for experimenters like us to buy, but the Chinese have come to our rescue by cranking out brazed plate heat exchangers by the millions.


Now, it turns out that making beer at home has become a popular hobby by people whose love of beer often exceeds their income. So to support these people in their quest for cheap beer, suppliers of the paraphernalia for beer making have started offering cheap brazed plate heat exchangers for sale on ebay.

This is where we come in...

I bought two for $70 each for my first prototype heat pump and they worked great, beyond my wildest expectations. Now, a couple of years later, I'm building a bigger heat pump and I just bought two more heat exchangers from the same ebay guy, and the new HXs are 50% bigger and @ $79.95 each they are cheaper per BTU. As a bonus, some of the HXs are now even available with sweat fittings for brazing refrigeration line onto. If you don't find exactly what you want, he can do custom orders.

I couldn't be happier if I was actualy drinking beer!

-AC_Hacker