great article in Solar Pro magazine about space heating

michael_34

Some great ideas in this article.

Mark Eatherton

Nice article, but....

The details are not complete and don't show the solar source, but if the solar collectors have a potential for thermosiphon, when the auxiliary boiler is on, the collectors cold be dumping heat out their glass.



One of the authors is considered a Guru of Night Sky Re-radiation BTU's. Night sky re-radiation cooling is a great concept that I have been following for quite some time now. It obviously works better with an unglazed collector than it will with a glazed collector.



Be interested in what the solar source concept is. Drain back? Closed loop glycol?



ME

jp_2

radiation.evaporartion, convection? Hmmm

very good point mark.  you have cleared things up.



if a collector is cooling poorly with a glass cover, its not radiant cooling working , its trying to cooling convection  wise.  or if it cools better without glass, evaporation is having a good effect, with convection helping too, depending on humidity of course.



just think of it in an opposite manner.  take the glass off a hot water collector and the efficiency goes down, thus evaporation and convection are playing major havoc with the solar heating on the panel.



thus clear sky re-radiation is helping out in a very minor way here and your real coolers are convection and evaporation.



 you could do some approx calculation here too, similar to sq meters and possible output as when you calculate how much energy you can harness from the sun, just in the opposite direction.



remember, everything above absolute zero radiates heat, so-called nighttime radiation really occurs 24 hours a day, just at night, the sun doesn't get to play.



you could argue that the glass passes shorter wavelengths but not longer ones associated with cool objects but I don't think thats taking place here.



but the key here is, it could be roughly calculated directly, or indirectly.





jp

hot_rod

collector cooling

we have been doing a lot of data logging on system cooling, collector cooling, and tank cooling (re-cooling)



In collector and system cooling mode, the concept is this.. The tank reaches setpoint, let's say early in the summer conditions. Use 160F as a tank setpoint. the collector sensor is always monitored. IF the collector reaches 230F (adjustable) the pump will again activate to help protect the collector fluid from over heating. It will continue to do this until the tank reaches 200F. Then it shuts down and stays off.



Collector cooling OCC aims to keep the collectors at a safe operational temperature.



System cooling OSYC aims to keep the system operational for longer periods. In either mode, the tank setpoint (160F for example)is allowed to be exceeded.



So now you have the potential to have a tank at 200F. The tank cooling OTC can now be used. This works by running the pump to pull down the tank temperature. As you can see by the data logger this is usually accomplished within a few hours. The graph shows both collector or system cooling and re-cooling at work. Yes, it does pulse the pump a bit to cool the tank back down.



Our controls also have a Holiday cooling option. in this mode the setpoint temperature is replaces with an even lower tank temperature, 110F is the factory default. Now the tank is pulled even lower by the re-cooling effect.



Another overheat protection sometimes used for summer vacation periods is to lock open the checks valves ALLOWING thermosiphoning to cool the system down at night.



Or you could run the pump 24/7 during vacations periods.



If you know a system will experience frequent no load conditions, drainback starts to look a lot more attractive.



hr

Mark Eatherton

Interesting stuff for sure HR...

I'd be interested in seeing what a metallic, unglazed BCO absorbers potentials are. I don't think we should overlook ANY energy savings potentials.



Is that a HOBO data logger :-) Output format looks familiar.



Maybe Caleffi could be the front runner in the radiant cooling business,eh?



Thanks for contributing.



ME



jp, Nice to see you stranger ;-)



ME

hot_rod

no doubt

an un-glazed collector would lose energy better. But the glazed would collect better, in cold conditions. Would it be cost effective to collect with glazed, and dump via less expensive un-glazed?



I think a well designed drainback, water not glycoled filled, still would win the race as most efficient system when compared to others. Simple too.



I have seen pictures of the pool type collectors used as dump heat exchangers. I remember seeing pictures of Cedar Mt. jobs done that way.



Our new Plus controller now has and arrangement for heat dumping, better know as load shedding or heat diversion.



It charges the tank to the max temperature, but only "sheds" when the collector goes to it's max temperature factory setting of 230F, adjustable to 320F.



All is well; here, fish biting yet?



hr

Mark Eatherton

Ice off...

Should be happening , if it hasn't already, this week. Then the action REALLY picks up.



I still owe you and your bride a weekend at Hydronicahhh. Make sure and make your reservation early. Schedule is filling fast :-)



Keep up the great work.



ME

Fortunat

the problem with the recooling functions...

HR,



Nice Data.

These functions in the Caleffi control, which I assume work just the same as the ones in the RESOL controls, are a great way to minimize system overheating and the time spent in stagnatino.



My one complaint about the control is the following:



By turning on the OREC (recooling function) and OCX (collector cooling function) (which I guess you call OCC and OSYC), you allow the control to ignore the tank maximum which you program (in RESOL called SMAX).



As you note, that SMAX becomes the temperature at which those other functions start working, instead of the hard maximum temperature limit. At this point the hard maximum temperature limit is the one which is hard coded into the controller, and i think it is 203 degrees F.



In our (unpleasant) experience, because of thermal lag and sensor placement etc, this 203 degree maximum limit is not always low enough to keep a tanks TRV from blowing off, dumping 80 or 100 G of 200 degree water into the basement.



If I had one piece of feedback for RESOL it would be to allow that 203

degree hard limit to be lowered in software, but currently it can't be. So we've found that we have to choose between using these ReCooling functions and having a safe and reliable tank high limit that is sufficiently far away from the relief setpoints.



Given the downside risk of the TRV blowing off (and having experienced it half a dozen times), we've mostly stopped using the recooling functions at this point, except in places where we are certain that the recooling will be sufficient to keep the tank from ever getting above the high limit (which is much easier with flat plates than with evacuated tubes).



Best,



~Fortunat



www.revisionenergy.com

Mark Eatherton

Fortunat...

When you say TRV, I assume you're talking about the Temperature and Pressure Relief valve, which industry refers to as a T&P relief.



In the closed loop heating lexicon, a TRV is a beast of a completely different color, used for controlling flow through a heat emitter, and it stands for Thermostatic Radiator Valve. Just trying to keep from confusing the newbies visiting this board :-)



Your other points are well made and taken.



ME

Fortunat

like you said

Mark,



Yes, I meant T and P. thanks mark.



I don't know why I wrote 'TRV', except that my brain is mush on Monday morning and I was just finishing up a heating system quote with panel radiators and TRV's.



So yes, the T and P blows off...not the TRV....duh.



and note that when the T and P blows on pressure (like if you undersize and expansion tank), it just burps enough fluid til the pressure is again ok. When it blows on temperature, as in this case, it dumps the entire tank..or very close to it.



In an unfinished basement it is very unpleasant. In a finished basement, it is terrible. On an upper floor it is absolutely unbearable...and can really ruin you day/week/month.



~Fortunat

www.revisionenergy.com