@jonr: Thanks! Very helpful.

@NRT.Rob: RE the mixing valve - the plumber I have been working with most recently also wondered about the mixing valve. He had me turn it from MAX down to 3 (on a scale of 1 to 10/Max). Interestingly, at first when I turned it to 3, the pressure in the system on the tank side of the mixing valve went up by a few PSI. But the temperature of the glycol loop did not change at all. That struck me as odd. Surely if I turn down the mixing valve then the temperature of the glycol loop should also go down....it did not.

I will drop the temp to 120 in the tank and see what happens. Can you explain to me why I might find the glycol temp go up if I turn the tank temp down?

I will try the alphas at the vertical 1 line setting. That would be so incredible to be able to get the system to work at this setting.

@ICFHybrid:

I am very near to Salt Spring. I will definitely think about using water instead of glycol. Good to know about how much more power glycol uses. Now, I have generally not kept the house heated when I am not there which is about 50% of the time. A few times a year it does get below 0C around here and we get some snow. Would it make sense to keep the glycol in that case?

I'll look into the borescope.

If I was going to descale the tank....it's 80 gallons so that is a lot of water. Would I just pour vinegar into the tank and then fill it with water? That would be an awful lot of vinegar....


Thanks!!!

If the mixing valve is not installed correctly, then as it heats up it may close off the hot leg from the radiant , rather than providing a smooth mixed temperature like you want.

-if you were pulling from the cold leg instead of the mixed leg, you'd recirc the radiant without adding much heat (but you might get some, these valves don't always close completely).
-If you pull from the "hot" leg, it would stop flow nearly entirely or maybe cause the pumps to pull from the other heating zone instead.

I am just skeptical that you are scaled up so badly that a 160 degree tank can only produce 86 degree water. that would be pretty incredible. of course we're in the land of "equally unlikely options" here but what can you do. next step, for me, would be to ask for pictures or a sketch of the system to make sure we're not missing a very important piece of piping or what have you...

don't bother removing glycol you already have installed: you can just turn the temp up a little more and whatever issue there was is taken care of. all else equal, no glycol is best but it's really best if you avoid buying it in the first place. but that's an issue to deal with AFTER the current problem is addressed in either case.

Bluelagoon-

Yes, I surmised that you didn’t have a very good designer or a good contractor…sorry to hear that. Regrettably, that is all too common and results in hydronic radiant floor heating getting a bad reputation. This is why I continuously advise people to apply due diligence when selecting their hydronic radiant floor heating design/installation team and I always recommend a licensed PE for the design and a licensed contractor for the installation. My responses to your specific questions follow:

1) Would raising the temperature of the hot water tank even higher than 160F make a difference?

Not the difference you want. If you elect to use your Grundfos at the low wattage settings, you will need to increase your supply temp by adjusting your mixing valve to achieve the target return temp as I previously described.

2) Is having the hot water tank at 160F vs. 120F costing me more propane to heat it? I would honestly rather have it at 120F but only because I imagine it is costing me more propane to heat…

Yes, heat loss is proportional to the difference between the water tank temp and room temp where your tank is located. If your room is at 70 F, this difference is 90 F @ 160 F and 50 F @ 120 F. So @160 F your heat loss is 80% more than at 120 F. Heat loss is also proportional to the insulation R-value of your tank. If your tank is well insulated like it should be, even this 80% increase in heat loss may not be very significant. If the tank is located in an area that you actually want heat, this additional heat loss may be okay. If it is not, this heat loss is indeed wasted propane. However, there should be no need to operate at 160 F unless you have a bad scale problem. Again, I would first recommend increasing your supply temp by adjusting your mixing valve to achieve the target return temp as I previously described.

3) How could I set the system up to use the least amount of power for pumping? Some of you have suggested I could run the Grundfos Alpha at 8W each which would be like a dream…

I would recommend first increasing your supply temp before experimenting with the pump settings. If you are successful with increasing your heat gain, you can then work on optimizing the pump settings and the allowed circuit temp drop.

4) How likely is it that scale in the hot water tank is causing me loss of efficiency? And if so, how to de-scale it? (I provided a link to the tank specs earlier.)

Very likely given that you have operated for 6 years with hard water. I would recommend consulting with your tank manufacturer or hire a licensed plumber to properly flush the tank
.
5) Would switching to water from glycol help me at all?

Yes, you will see a slight increase in heat transfer capability and a slight decrease in dynamic head loss resulting from hydronic friction in the circuits that results from your pumping flow rate. However, you will have to trade this benefit versus the risk of freezing your circuits.

Relative to your situation of having your tank located 10 feet below the circuit runs, YES, this is an additional 10 feet of static head loss that pump has to initially make up in addition to overcoming the dynamic head loss from hydraulic friction in the circuits that results from your pumping flow rate. To help with your understanding, think of the circuits in your floor as heat conveyors. You can convey more heat and you can achieve a higher room heat gain by pumping at a higher flow rate or by using a higher supply temp or by doing a combination of both. A higher pumping flow rate will result in a smaller allowed circuit temp drop. However, a higher pumping flow rate will result in higher hydraulic friction and will require higher electrical power. To achieve both your heating and power objectives, you will ultimately need to use a higher supply temp and the minimum pumping flow rate that results in an allowed circuit temp drop that you are happy with. As I discussed previously, if the flow rate gets too slow in your circuits, the flow will become laminar and you will suffer from reduced heat transfer capability.  This results from colder water stagnating next to the circuit wall which then inhibits the heat transfer thru the wall and to the concrete slab.  This will be very obvious if and when it happens.  Please also keep in mind when making adjustments and accessing results that it takes several hours for a concrete slab floor to reach a stable temp.  Presumably, this has been the tank location since day one and NOT something that has changed. If so, all of this should have been accounted for in the original design and you indicated that your system worked well at day one with the original pumps.

I'm confused. Are you saying that a pump with 10 ft of head can't be used if the system is more than 10' tall? even if it's a closed and pressurized system such as this fellow's? Cause that's what it sounds like you are saying.

Agreed: closed system, static head doesn't effect pumping costs.

Laminar vs turbulent - not such a sudden change and numbers I've seen indicate not that big a difference in overall heat transfer. Would be interesting to see more real world data.

Mixing valve - just check the temp as the glycol exits the tank and before it hits the mixing valve. High means the valve is not working right, low means the heat exchanger isn't.

Posted By NRT.Rob on 27 Dec 2012 06:29 PM
I'm confused. Are you saying that a pump with 10 ft of head can't be used if the system is more than 10' tall? even if it's a closed and pressurized system such as this fellow's? Cause that's what it sounds like you are saying.

Yes, that is exactly what I am saying.  If you have a pump with less head than the circuit elevation it has to reach, it will initially not be able to pump to that elevation and you will never get a closed system.  You will first have to create a closed system using another pump which I expect even you would know...but you continue to amaze and entertain me...  If Bluelagoon is going to be opening, draining, and flushing his system himself, this is something he will need to consider and address if necessary.  Bluelagoon already described his hellish experience in trying to get this problem resolved.  We wouldn't want him to have to hire yet another expensive, unlicensed, clueless technician again just for making this simple mistake now would we?

IIRC, the older Thermomax tanks were a real problem because they had quite small heat exchangers (they are/were locally made in BC). I had an issue similar to the OP where the I knew solar panels were producing the correct amount of heat but it couldn't be transferred to the water effectively. This may be part of the problem. If the OP is on Gabriola Island or there abouts, 20% glycol would be all that's needed. What percentage was installed?

Oh and the 10' vertical height being a problem......bollocks....it is not 10' of static head, it is not an open loop system. The restriction is only that of 20' of piping + elbows

Can the OP take a pic of one of the manifolds so we can see the number of loops and maybe even a flow gauge if there is one on the manifold.

Posted By sailawayrb on 27 Dec 2012 07:27 PM
Yes, that is exactly what I am saying.  If you have a pump with less head than the circuit elevation it has to reach, it will initially not be able to pump to that elevation and you will never get a closed system.  You will first have to create a closed system using another pump which I expect even you would know...but you continue to amaze and entertain me...  If Bluelagoon is going to be opening, draining, and flushing his system himself, this is something he will need to consider and address if necessary.  Bluelagoon already described his hellish experience in trying to get this problem resolved.  We wouldn't want him to have to hire yet another expensive, unlicensed, clueless technician again just for making this simple mistake now would we?

WOW! really????? wow. you make this way too easy. I'm starting to feel kind of bad, I don't really want to pick on you, but you are just so incredibly ignorant here that I just can't let it stand for fear that someone might read your words and believe them.

If ONLY there were a source of water nearby under enough pressure to reach up to the tippity top of a house (or maybe a few feet below the highest shower head in the home)! If we could ONLY find a way to get water up that high, then we could use smaller pumps in our systems for decades instead of upsizing them for the initial fill! HOW CAN WE SOLVE THIS CONUNDRUM?

NO WAIT. WHAT IF SOMEONE INVENTED A... I DON'T KNOW... SOME KIND OF A "PORT" OR "VALVE" BY WHICH WATER COULD BE INTRODUCED AT A HIGH POINT IN A SYSTEM???? MAYBE EVEN BY HAND!!!

Please, someone, there has just GOT to be a way! anyone?? anyone!?!?!?

someone call a PE! they will surely know how practically every residential hydronic system in america gets filled with water, won't they???

Wrong on head there big fellow.
The supply return of 3/4 or 1 inch pipe diameter pipe to 10 feet or so up, down or sideways in a closed system is irrelevant, .0028 head per foot on 3/4"
the effective head number in this case is the still un known loop length of 1/2 pex.

Dan

Rob,
I found what you are looking for right on my web site!!!
Webstone purge and fill valve, you can do this now from the boiler room way down below...
Have your coffee in peace and quiet in the ol mec room!
Link http://www.blueridgecompany.com/radiant/hydronic/672/webstone-valves
Dan

thanks for ruining my patent dreams dan!!!

I just can't imagine it getting cold enough long enough to freeze your slabs and the radiant within, unless the designer ran a loop outside over your porch or something like that. There is a terrific amount of residual heat in a house and slab. You could be sure by turning the water temp way down and setting a timer to circulate the loops every so often. If you are dialing this so far down as to be counting every watt, you owe it to yourself to try the water.

Seems like you should be able to get a plumber to come over with an inspection camera, but there is going to be a fair amount of time involved in taking the tank down and emptying it for the viewing. If you have to, you can descale using citric acid. The concentration to use for stainless would be 2% -5% by weight. 2% is 2kg per 100 liters. With a tank volume of 300 liters, I'd get a large plastic garbage can to recirculate in and plan on 350-400 liters total. That means up to 8 kg of citric acid. You can get it for about $150, probably less depending......Then, you will need some hose, adapter fittings and a little plastic transfer pump from the hardware store. If you have additional problems with iron deposits, you may have to adjust the mixture.........

Yes, the Webstone valve is a wonderful device although Bluelagoon may not need to purchase one. With any luck his system was designed with maintenance/servicing in mind...although this may be a bad assumption given what he described... If his system has make-up-water, he may already have a quick fill valve and, if so, hopefully also a back flow valve too since he has been running glycol. As I mentioned previously, Bluelagoon has already indicated that he successfully opened, flushed, filled and purged his system. So this should not be an issue for him and he should already be very familiar with how to properly do it.

Bluelagoon, some photos of your installation would answer many questions.

ICF is right about the glycol.

Rob is right about tank output. The easiest and most accurate way to determine your tank is scaled is by comparing factory specs to the temperature differential.

One smart guy at the desk is worth 100 "plumbers" in the field.

There seems to be some uncertainty about flow rates and temperatures and whatnot. At some point, it really is just more definitive to drain the tank and take a look for yourself. Especially when the people who can psyche it out are limited and you're not 100% sure who you can trust.

At this point, though, I will echo Rob and say that bluelagoon should take a few images of his setup, post them here and stand by to answer questions.......