Gravity/Convection circulation questions

Stew_5

I live in a remote area. My water supply is from a creek and the static pressure is 32psi. As a backup water supply I have a storage tank in the loft. When I'm running on the storage tank the psi is about 4 lbs. My domestic hot water is heated by coils in the woodstove, in a closed loop to an 80 gal. water tank sitting right next to the stove. I get all the hot water I want and it circulates quickly and quietly.

I'm working up to my question: Whenever I'm on the storage tank system and my hot water tank heats all the way up (about 130 to 190 degrees), it starts to hammer like crazy. It sounds like maybe I'm making steam in the coils. As the water temperature increases, the hammering,banging bubbling gurgling gets longer and louder. Usually I have to valve off the coils and drain them (VERY CAREFULLY!!!), or I won't get much sleep.

The only thing that changes here that I'm aware of is the static pressure. So does a higher pressure mean faster better gravity circulation? Why am I making (I think) steam in my coils under low pressure?? Why doesn't it just circulate nice and quietly like when I'm on creek pressure?

When I build my radiant floor heat system with gravity circulation, how much pressure should the glycol be under?

Al Letellier_9

hammering

the higher the pressure, the more heat it takes to make steam. I think you've answered your own question, but answer mine. How are you going to make a gravity radiant system work? A new concept to me.

zeke

under

Remember, if the tank is at 4 psi and 34 feet of water is 14.7 psi, at 10 feet below the tank, the nominal pressure is less than atmospheric. Coupled with the pressure differential across the pump yo will get an even greater vacuum, so the 190 degree water will tuirn to steam and cavitate. You should raise the pressure to significantly higher than 4 psi or lower the water temp.

jp_2

higher pressure higher danger

boy, you talk about the dangers of woodstoves?

you are creating a steam bomb!

reduce the temperature somehow, dump that heat.

Stew_5

Steam Bomb?? I hope not!

Please correct me if I'm wrong, but I thought I had two safeties factored in: First, the tank/resevoir system is open to atmosphere, so the coils do create steam and hammer, the pressure is immediatly relieved to atmosphere. The pressure does jump around a bit while hammering, but even then, it doesn't get very high. Second, I have a standard water heater temp/pressure safety valve on the top of the heater tank. It has never popped and I've been using this system for 15 or 20 years...

Stew_5

Gravity radiant heat; Impossible or Improbable?

Well, I'm trying to figure out if a gravity radiant floor is possible. I hope it's possible because I live in a remote area and have to produce my own electricity. Every watt is precious, and even if something uses "very little" electricity, believe me, it adds up FAST when you consider that little draw is running 24/7.

So supplying a little power for a control system that runs intermittantly is very different from supplying even less power for a very very effeciant circ. pump. Plus I don't want to be without if the battery dies or the inverter dies or the charging system (wind, hydro, solar) decides to go on vacation. When I have to maintain or repair those systems, I don't want to be shivering.