Solar Hot Water Control, Heating, Heat Dump Questions...

jb_14

Hello -



I am putting together an oversized solar H2O system in Virginia to provide some space heating benefits as well as domestic hot water.  As a result I will need a good heat dump strategy in the summer months.  Also I am seeking a simple way to select/control my heating system and choose between my prestige boiler and my 'solar boiler' depending on the presence of solar heated water.



I'm attaching a diagram - and here's a link as well to my system layout:

<a href="http://s597.photobucket.com/albums/tt52/jb_va/solar%20h2o/?action=view&current=SolarH2OSchematicDiagramjpg.jpg">http://s597.photobucket.com/albums/tt52/jb_va/solar%20h2o/?action=view&current=SolarH2OSchematicDiagramjpg.jpg</a>



For the solar h20 system control - I am looking at the caleffi isolarplus controller with 4 sensors 2 triacs (relays) for a pump or a 3way valve.  <a href="http://www.caleffi.us/en_US/caleffi/Details/News/files/257_Series.pdf">http://www.caleffi.us/en_US/caleffi/Details/News/files/257_Series.pdf</a>



Here's what my system does, and what I want to do:

1. My prestige solo boiler is controlled by a Taco 6 zone switching relay heats my radiant zones normally via primary-secondary piping and closely spaced tees - and my Smart-SME is my indirect hot water tank - that is normally heated by the prestige boiler for my domestic water.  The Smart SME 60 if you didn't know is a 60 gallon stainless domestic tank - within - a 100 gallon steel outer tank that contains 'boiler water' normally heated by the prestige.  At the bottom of the SME is a coil for the closed loop solar piping circuit running through my 2 - Apricus 30 evacuated tube collectors up on the roof and bringing that heat into the SME via the coil.  The prestige boiler is piped to the SME by the upper tappings.  The SME is connected through closely spaced tees to my primary-secondary central heating piping via lower tappings as well.



SME

<a href="http://www.triangletube.com/documents/23/SME_Literature.pdf">http://www.triangletube.com/documents/23/SME_Literature.pdf</a>



2. When solar heat is available the caleffi controller will activate the solar Loop glycol-water circulator and solar heated glycol-water will circulate through a SME coil in the bottom of my indirect tank- heating the 100 gallon outer 'boiler water' tank - and thus heating the inner domestic tank. 

3. In the winter (during sunny  milder days near fall or spring) if there is sufficient heat in the outer and inner tanks (detected by sensors in those locations) and there is a call from a zone to the Taco SR506 for heat - then I want the Prestige Solo Boiler to be bypassed - and have the heated water in the SME outer tank to be circulated through the closely spaced tees to my central heat piping system via the Solar Heating Circulator.  

4. When sensors indicate a lower set point has been reached in the SME outer tank (conserving some heat for domestic priority ), then I want the Solar Heating Circulator to be deactivated - and have the Prestige Solo Boiler - take over the central heating duties.

5. The caleffi controller has 2 electronic relays - one for the solar loop circulator - one for the heat dump 3 way valve - or perhaps use the second one for control of the solar heating circulator - however when this cirulator is activated I need to de-activate the prestige boiler.  (and in this case I would try to find an automatic heat dump valve that will open if a certain high temperature is reached in the solar glycol loop - presumably during hot summer days with low demand. 

6. My solar loop heat dump will be a coil of copper buried several feet under my porch -  through the wall from my basement boiler room and carefully backfilled to give up heat to the ground during summertime when excess heat is collected.  The solar glycol-water fluid will be diverted to flow directly through this coil to dump heat until the solar loop or outer tank are at a reduced temperature set point.  (best to have this heat dump before the tank or after the tank?)

7. Is there a simple single pole double throw type of relay or switch that can respond to one of my caleffi pt1000 sensors - and 'choose' between the SME/Solar 'boiler' OR  the prestige boiler - during a call for heat?

8. I've looked at the Heat Timer TSC two stage set point controller - to control my boiler and solar heating as essentially '2 boilers' - which looks like it would work - but it seems excessive and expensive that I'd need a 3rd controller along with my Taco SR 506 and Caleffi iSolar Plus. 

9. Is there a relay that can detect the operation status of the solar heating circulator (that has been activated by the Caleffi) and thus - bypass the call to the prestige boiler - and when the solar heating circulator is off - then the prestige boiler would answer the call for heat - until such time as there is sufficient solar heat and the 'bypass' would be repeated.



Sorry such a long post.  I am doomed as an engineer to overanalyze things - particularly new areas I am learning and have found much good discussion on heatinghelp.com and the wall.  Thanks for any advice or thoughts!

hot_rod

consider

flat plate collectors that could serve as your heat dump emitter. The new I-solar plus contoller has a system cooling function that will run the pump after the sun goes down to cool the tank back down IF it has gone beyond 200F.



By doing this you don't have to dig up the yard and sacrifice expensive copper to the earth from whence it came



It also frees up that second relay to run a 3 way valve that choses between the tank or boiler as the heat source for the radiant.



To assure you always have DHW, you really need to have the boiler fire the top of that tank. This limits the solar contribution however, if 30 gallons, up top is always hot.



Another method is to put the boiler DHW call on a timer. If you have a consistent schedule, time the boiler DHW mode off at 8 or 9 AM and back on when needed. Get a timer with a 7 day schedule so weekends could be programed accordingly.



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Thanks HotRod - And my control question

So I've already got the evac.tube collectors from a closeout - and I'm concerned about dissipating the excess heat during August - perhaps when we are at the beach or something - so I think I need a more active dump - like my ground coil.



I am essentially stuck with  the arrangement I describe - so I wish to control it most efficiently and with the least additional controllers, etc.



I agree I hate the thought of putting a lot of fine copper in the ground and dumping heat that I'm harvesting (maybe I can sell hot h20 to my neighbors - ha ha)  - but until I can rig up something innovative such as adsorption cooling, or dryer use of the heat, or electricity generation from the excess heat, etc. - I'll need to dump it because my 2-30 tube collectors will certainly exceed our usage on the hottest, sunniest days - and of course when we're gone in the summer.



On my control question - I've already got my solar tank and boiler separately conencted to my primary central heat piping by separate piping and closely spaced tees - so I'll need to control the solar heating circulator as a separate 'boiler' - and bypass the prestige - when the solar heat is available.  Is there a fairly simple way for a relay or SPDT switch to use 'either or switching' - so I can  control the solar heating circulator to the central heat primary piping and at the same time - by default - open the XX terminals to the prestige from the Taco SR506 switching relay  - so  when there's a call for heat - the boiler will respond - unless there is sufficient solar heat in the SME tank (read by a sensor well down near the solar coil) - and in that case the simple set point controller/tstat reading that temp. will activate the solar heating circulator - and by it being 'activated' the connection from the xx terminal on the switching relay will be opened - so the boiler does not answer the call.  then when the solar heat is exhausted (by predetermined set point) the solar circ. will deactivate - and if there is still a call for heat - the connection from the xx terminals to the prestige will be closed and the boiler will finish the job.



Heat Dump - Is there a very basic non electrified 3 way valve that can be set to open and divert the solar loop flow (at its hottest from the collectors before the tank) through the heat dump when the tank reaches a certain temp?  If the sensor was in the return to the collectors after the tank and was very high (or sense the tank temp directly)  - 190 or 200 - that would indicate that the tank was at its maximum temperature (due to low demand and lot's of solar energy say) - and the diversion would be in the hot supply from the collectors - to dump heat before reaching the tank - or perhaps bypass the tank altogether until it drops sufficiently.



I'm looking at the heat timer tsc - to use a tank sensor and choose between the prestige boiler and the 'solar boiler' based on the temp in the solar heated lower part of the tank.   But that's still $1xx plus sensor.   Is there an even simpler way to toggle between the boiler and the 'solar boiler'?   Could I use the taco sr506 and it's priority in some way? 



I'll probably use the Caleffi 2nd triac/relay to control the diversion valve - unless there's a way to control the diversion valve like a mixing valve without needing power.



sorry to go on so long.  any addional thoughts would be much appreciated.



Hot Rod - you are the Caleffi Webinar trainer at times?  Nice work - very instructive as I do my first solar thermal system.

hot_rod

a number of ways to do that

With only 2 outputs on the I-solar Plus you need to get creative to run 3 different functions. Here is a drawing and wiring concept from I-dronics 6. We use the first output of the I-solar Plus for the solar, always. The second output would switch that 3 way valve to select from solar or boiler heat. But now you need to build the dump logic. Remember you should have a mixing device on the supply to the radiant from the solar. With that tank to collector ratio, you could see some temperatures much too high for the heating zones. Outdoor reset in a nice feature on that "device".



The next drawing shows #5 as a heat dump with the 3 way valve.



Better yet is the I-solar Plus version 2 control. It has a arr 10 for heat dumping. This works better as it only dumps whenn the collectors reach a high limit, not when the first loas satisfies. it also now has a timer on the OTC (option tube collector) feature. The TC (tube collector) function pulses the pump to flow some fluid across the sensor in the header piping so the control knows the array has some energy to give. Before it could trigger the pump at nightime and run the system.



Until we get our 4 output control, you will have to build the 3rd function. Any setpoint controller will be able to watch the tank temperature and run the second 3 way valve. If you get a double pole double throw version you could use the second set of contacts to drop out the boiler call, etc.



It could also be done with a flow switch. When ever the solar loop is flowing to the heat load, the flow switch could prevent the boiler.



BUT, in your case you will need to keep the tank warmed by the boiler for no-sun days or weeks, so the boiler needs to be left online.



I think that is what you are trying to accomplish.



You will have a limited solar contribution when the tank is always maintained by the boiler, so you may be dumping heat more than you would like. A second solar storage tank could be a big plus, control wise and to maximize the solar energy all those tubes can harvest.



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hot_rod

a number of ways to do that

With only 2 outputs on the I-solar Plus you need to get creative to run 3 different functions. Here is a drawing and wiring concept from I-dronics 6. We use the first output of the I-solar Plus for the solar, always. The second output would switch that 3 way valve to select from solar or boiler heat. But now you need to build the dump logic. Remember you should have a mixing device on the supply to the radiant from the solar. With that tank to collector ratio, you could see some temperatures much too high for the heating zones. Outdoor reset in a nice feature on that "device".



The next drawing shows #5 as a heat dump with the 3 way valve.



Better yet is the I-solar Plus version 2 control. It has a arr 10 for heat dumping. This works better as it only dumps whenn the collectors reach a high limit, not when the first loas satisfies. it also now has a timer on the OTC (option tube collector) feature. The TC (tube collector) function pulses the pump to flow some fluid across the sensor in the header piping so the control knows the array has some energy to give. Before it could trigger the pump at nightime and run the system.



Until we get our 4 output control, you will have to build the 3rd function. Any setpoint controller will be able to watch the tank temperature and run the second 3 way valve. If you get a double pole double throw version you could use the second set of contacts to drop out the boiler call, etc.



It could also be done with a flow switch. When ever the solar loop is flowing to the heat load, the flow switch could prevent the boiler.



BUT, in your case you will need to keep the tank warmed by the boiler for no-sun days or weeks, so the boiler needs to be left online.



I think that is what you are trying to accomplish.



You will have a limited solar contribution when the tank is always maintained by the boiler, so you may be dumping heat more than you would like. A second solar storage tank could be a big plus, control wise and to maximize the solar energy all those tubes can harvest.



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jb_14

Solar Hot Water for domestic and radiant heating

Thanks Hot Rod.  It is a good point about wanting to maximize the solar input into the tank - and if I"m taking heat out to the central heating - I need to develop some logic to keep the boiler from heating the tank back up - when solar will be available to do the job. 



Adding more storage sounds like a good idea particularly in warmer months to minimize dumping.  What do you think of using a regular gas hot water (heater) tank as a solar heated domestic water auxiliary storage tank (with the burner disabled/not hooked to gas) by using a hot water circulator between the solar tank and the (turned off) water heater (circulate domestic hot water to heat up the auxiliary tank when the solar tank reaches its set point)?



In colder months, perhaps some timer or time of day function on my set point controller that can block the call to the boiler to heat domestic water in the indirect when solar will soon be available. (Give the solar a chance to heat the tank up during the day - when normally there are few hot water loads after morning showers).  A flow switch on the solar circulator or the solar heating circulator, as well as checking the collector temperature (to detect the sun shining?) might be other ways to "choose solar" heating of the solar indirect tank whenever possible.



It will be interesting.  I'll give an update.



Anybody use the Heat Timer TSC Elite and have some success?



Anybody doing solar hot water for domestic and some space heating - using a boiler fired indirect - and have the boiler-solar-heating-domestic hot water - logic worked out - to maximize solar and keep the boiler from doing the work of the solar before the solar kicks in?

PBX

Connecting the Solar

You solar system sounds almost identical to mine and your issues are basically the same. As your posts with hot rod were in April, I am hopefull you worked out your bugs and would be interested in sharing your fixes. My system is set up pretty much like yours and my Solo 60 has been going through a bunch of propane heating 160 gallons just to heat 60 gallons of DHW! I've got a 60-tube Mazdon collector (2-30's in series) array that I'm trying to finish up the plumbing and control. I uploaded my system diagram. My current problem is trying to get a senor in the top of the tank (SLME 600) and there is no sensor well. So I have been trying to find out if the tank temp sensor/thermostat can be connected to more than one controller. I'd really appreciate hearing your suggestions.

Fortunat

details

Lots of tricky details to get right in solar space heating systems.



One good rule is to avoid heating the tank with the boiler whenever possible. One system we've used that looks a bit like what the original poster presented is attached.



We control the heating system with a Tekmar 363. It might be kind of overkill, but the controller is nice and smart. It will do variable speed injection from the solar tank into the heating loop trying to achieve a particular temperature based on the reset curve and then when the tank can no longer keep up it will switch and turn off the solar injection pump and start the boiler pump instead.



This isn't one of Tekmar's standard application examples, but it is fairly straight forward to make the controller do what we're asking it to. Let me know if you want a wiring drawing for the controller and I'm sure I can dig one up.



Best,



~Fortunat

www.revisionenergy.com

Gordan

Something useful to do...

...with extra hot water in a Virginia summer: dehumidify.



They now make residential dessicant-based dehumidifiers with models that use a gas burner and models that use hot water to "recharge" the dessicant wheel. Just an idea.



If there's ever a residential absorption chiller, that'd be a WONDERFUL use of all that extra heat.



Regarding the "basic 3-way non-electric valve" question, I'm pretty sure that any 3-way thermostatic mixing valve can also be used in diverter mode - you just plumb it differently (input on AB, output on A or B.) I believe I've seen ESBE docs that illustrate this configuration for charging stratified storage tanks.

hot_rod

a fixed temperature 3 way

with a fairly high temperature cartridge would work to shed some excessive energy.



I spotted this product with high temperature components. Remember the valve needs to be able to handle stagnation temperatures in the event of a pump failure or power outage. I'm not sure many "off the shelf" thermostatics would be rated for this. I see this brand has a whooping 400F max. temperature. That would be plenty for flat plate collectors, I've heard of evac tube systems exceeding that temperature?



I met a solar installer in the Chicago area a few years back that uses 3 way thermostatics like this and a piece of commercial fin tube along side the collector array for the dump "device"



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