Solarroofs.com system install

pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
Just got a Temperate System 3 from SolarRoofs.com and have a question about how I should or should not be connecting the return line from my existing HW recirc system which is connected to my gas water heater.

The system is an open loop with the quick connect package that is referenced elsewhere on this forum. The folks at Solar Roof suggest that the return from recirc system should be moved from the bottom of the tank to the top of the tank. The reason stated is that the collectors can be more prodcuctive if the water at the bottom of the tank is cooler and not warmed by the residual heat from the returning hot water......

I would prefer not to move that connection and am looking for someone to comment on my logic.

Presumably, the water in the water heater on most days will exceed 150 degrees and overnight there may be a 10-20 degree drop which will leave the temp at something greater than 120 degrees the next morning when the system starts to operate again.

If the water in the tank is still hotter than the setting on the gas heater, what advantage is there in moving the retun line?

Moving the line is not a huge issue, but the rationale for moving it is in doubt in my mind??? Appreciate you insights..............

Many thanks,
Nick

Comments

  • mike95490mike95490 Solar Expert Posts: 7,358 ✭✭✭✭
    Re: Solarroofs.com system install
    pcguy2u wrote: »
    The system is an open loop with the quick connect package that is referenced elsewhere on this forum.

    maybe a link to the other postings about it ? Do you have a sketch or schematic of the system. I can't possibly comment on it, till I can visualize it.
    My first thought would be, to fully heat the entire tank of water, not just the top half.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators Posts: 26,969 admin
    Re: Solarroofs.com system install

    Generally, with solar hot water, your desire is to get part of the volume (such as a 1/4 of the tank capacity) of water above some temperature (like 120F) for domestic use--rather than have the whole tank heated to 90F (same amount of BTU--but 90F to too cool for its intended use as domestic hot water).

    So--whatever their suggestion is (and I also don't quite understand the suggestion and how it would be implemented)--the intent behind it is to prevent stirring of the hot water tank (the electric pump used to move water through the collector will, to a degree, stir the hot water storage tank) and causing uniform temperature throughout the tank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Solar Expert Posts: 1,959 ✭✭✭
    Re: Solarroofs.com system install

    The quick connect system I installed replaced the drain bib. It has both the return and send in this split connector and the return was a long 3 foot 1/4" copper flex tube that in essance feed near the top of the tank and got the source from the bottom

    If you have seperate send/receive connections, the return should be near the top, so the hotest water is what the home recieves first. Energywise, it really doesn't matter but it will help in the winter months to deliever solar heated water without having to bring the entire tank up tempature wise
  • TelcoTelco Solar Expert Posts: 201 ✭✭✭✭✭
    Re: Solarroofs.com system install

    From that site:

    "This system circulates potable water through the collectors and then returns the solar heated water into the storage tank. The standard configuration uses a "Quick Connect" that replaces the drain at the bottom of the tank with a "coaxial" fitting. This fitting allows the solar collector feed and return line to share the same hole. Returning solar heated water goes through a center tube into the tank. The warmer solar heated water immediately rises. At the same time cool water is being sucked by the solar pump through the space around the hot return tube."

    It doesn't show pictures, but if I am visualizing it correctly they are counting on convection to move the heated water straight up while drawing in cooler water at the same point. Convection currents aren't that fast, so likely you're drawing as much preheated water in as you are cool water from the heater (relatively speaking). It'll take longer for the solar heating setup to heat the water this way, so you'll have to burn more power to do it than if the hot went into the top and the bottom only saw cool. It would do better to dump into the top of the tank than through the bottom, and you could likely go in through the overpressure valve at the top of the tank. Remove the overpressure valve, thread in a short pipe, thread a 3 way onto that, then put the inlet on one side and the overpressure valve on the other. Now I don't know how code will like having the overpressure valve share the same inlet, but I don't see any reason why it wouldn't work. That "coaxial" connector they describe is aimed more at selling a bolt-on kit than efficiency.
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Solarroofs.com system install

    The Quick Connect part which was referenced in another post has both the cold to and the hot from the collectors, causes water of both hot and cold temperatures to be mixed at the bottom of the tank. The hot return being an 18" plastic feed inside the 3/4" cold out connection.

    My concern is that if the water in the tank gets to be very hot, my recirc system could cause that very hot water to be sent to the home. I have attempted to make this a non event by including two tempering valves (see drawing below) - one for including cold water when there is a household demand and the other set differently in order to cause only the returned water to be recirculated or at least very little of the tank water. If I move the return to the top of the tank, the tempering valve for the return will potentially not have a sufficient differential for it to function properly????

    Or am I way off base here???? BTW, the plumbing part of the system has not been installed yet.

    Thanks again,

    Nick
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Solarroofs.com system install

    I agree with the idea of bringing the returned hot from the collectors into the tank at the top of the tank. And BTW, there is no storage tank on this system, just the water heater.

    I have figured out that I could rearrange the quick connect so that the 18" plastic pipe is fed into the top while the cold out is from the bottom of the tank.

    Thoughts?

    Nick
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Solarroofs.com system install

    I used to have a thermo-siphon solar/wood tank. It was mounted horizontally. It served a a pre-heat tank for demand tankless water heater. The problem in those days was the demand heaters couldn't modulate their temp so if the preheat tank was close to useable, the water heater would put out full btu's and the shower water was way too hot. It was find in the tub, but death in the shower.

    Most of the new tankless gas water heaters will modulate the gas valves so that the out going temp is a preset constant. (Takagi, Rinnai, Paloma etc. I don't know about Bosch or Noritz.)

    It seems if you are going to go to the trouble of solar water heat, you should take the next step and go to demand as well. I am planning on rebuilding the system with the new tankless heater, and I expect our annual hot water bill to be close to $0.

    T
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Solarroofs.com system install

    I know what a tankless demand water heater looks and works like but my ignorance is showing here. How do you integrate a heater like that with a solar system and more importantly, why?

    n
  • Solar GuppySolar Guppy Solar Expert Posts: 1,959 ✭✭✭
    Re: Solarroofs.com system install

    You don't need mixing valves and 18" for the hotwater return returns water almost straight up as small diameter jet exiting the tube.

    For sure, mixing valves are not needed, I have this system, now my previous home still in use 8 years later. did 100% of the water all except winter

    Even with a top return, the second that dribble of collect return water its the tank water, its almost instanlty cooled to the water in that area of the tank

    Just install the system as the instructions are, and if it happens to not work as you like THEN make custom changes, I doubt you will need to do a thing.

    Make sure you set the gas thermostat a good 20 degrees below the differential controllers setting, or you will be wasting gas needlessly

    If you do want to improve the return, I'd just add some lenght to the 18" return, but still use the lower bib location as it was designed for
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Solarroofs.com system install
    pcguy2u wrote: »
    I know what a tankless demand water heater looks and works like but my ignorance is showing here. How do you integrate a heater like that with a solar system and more importantly, why?

    n

    A pre-heat tank, acts like a large spot in the incoming pipe to the water heater. As you draw off hot water, new cold water flows into the tank, (replacing the preheated water), and then to the demand water heater. A modulating demand water heater will add ONLY the amount of heat required to bring the water up to the desired temp.

    For example, your street or well water comes into the house ~50f average. A normal water heater will heat the entire volume to say 112f.( A 50f temp rise). In a tank type, obviously you are heating an enormous amount of water and much of that heat is lost to the room. (Not really a problem in the heating season, but there are more efficient ways to heat the room. In the cooling season why add heat to the room at all?) A demand water heater will heat only the water that is used so there is much less waste. (it also captures more net BTUs than a tank type).

    So with a solar preheat tank, the water comes in at the same 50f. The sun heats it to say 100f. Turn on the tap, and the demand water heater only needs to heat it the 12f to 112 for a savings of ~75% of the BTUs needed to heat the water.

    Make sense?

    Tony
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Solarroofs.com system install

    If I understand that correctly, the greatest advantaage to doing it that way occurs during the winter months?

    n
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Solarroofs.com system install

    No, to the contrary. The advantage is all year round depending on the sun on your collector. You might, for example pick up 10f on a average winter day, and 100f on the average summer day. Of course it all depends on how a system is sized, located etc.

    The point is, the demand water heater is used to SUPPLEMENT any preheated water. Any preheated water comes as the bonus, by having to be heated less.

    Tony
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Solarroofs.com system install

    You guys are great - here's a little update on the system.

    First of all, the system normally heats up to about 112F on a sunny 62 degree day here in Bodega Bay CA. Just perfect for most needs.

    Overnight, with the gas water heater on pilot for understanding how this thing really works, there is about an 18 degree cooldown. This works fine if you dont need to take a morning shower and for the moment, I'm showering in the afternoon while there is time to reheat the water used for the shower.

    But I'm thinking about winter and cold foggy days and how you can't automatically control the gas part of a gas water heater - I did try several methods and the way the thermostat is constructed, it defeated every attempt.

    So, since I want to be able to heat water for those not so warm days and to be able to heat it at the time of day deemed best (by the bosslady), without having to do any manual changes, I have ordered a Takagi tankless (small one, no pilot) to use with a timer/clock and with my recirc pump as the means of firing it up.

    I should be able to set the timer a couple of times a year (for the obvious time of day that there won't be any Sun) and maybe even for a morning shower:D

    The Takagi has the ability to turn on and off at almost every temp between 95F & 122F using a differential test for about 5 degrees between two internal thermistors.

    So thanks to you icarus for pointing this out - it turned out to be the answer to a number of conundrums.

    Nick
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Solarroofs.com system install

    I'm glad I could be of help. Once question however. Why are you going to use the Takagi on a timer to heat shower water? Why use gas to bring up the water in the hydronic, when the sun will bring it up later. It seems (if I am reading you correctly) that you could just use the hydronic for pre-heat, run the pre-heated water through the Takagi for the shower.

    Am I missing something here?

    Tony
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Solarroofs.com system install

    It isn't so much for shower water as being able to turn it on programatically or automatically, especially in the winter when I suspect the system is not going to be terribly useful. One other good reason is the lady of the house.

    I have the gas usage down to about 1/4 gallon per day. Not sure where that's going when the takagi is running - all in the interest of the carbon footprint.

    One other thing is that my water heater and collector are 135' from the master bedroom, so the only useful way to get hot water there is with a recirc pump, and that will serve as my demand/signal for the Takagi. At least this way, my options are open and I have some degree of control - something I couldn't do with the standard gas WH thermostat.

    n
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Solarroofs.com system install

    I admit I can be a bit thick sometimes, but I am still not clear on a couple of things.

    First, are you going to use the Takagi for supplimental heat when the sun doesn't heat it enough? There are specific Takagi, Rinnai, and Bosch heaters made just for that purpose.

    Second, since you have to send the water 135' to the shower you have some other options. The simplest would be to install the demand water heater nearer the use,,in other words nearer the shower. (They take up little space, and can be installed almost anywhere you can get a vent out, either up or out)
    By doing this you could still use the preheated hydronic water, it is just that the 1st 135' worth would be colder than the rest.

    You could also do a circ line to the bath that circulated below the threshold that the Takagi would turn on. (somewhere around .5gpm if I remember) A 1/100 hp pump running a tiny 1/4" return line wouldn't draw much electricity.

    I think that if you have the "blank slate" of doing the house plumbing you should think through the options carefully. It just seems to me intuitively, that heating the entire hydronic system for the early shower when the sun will heat it later is not real efficient.

    Just to throw another idea out there, You could consider using a combination boiler like a BAXI that has a hydronic section, as well as a domestic section. Both can be plumbed through a solar hydronic system. They are also quite small and can vent a number of different ways.

    Good luck, I hope I am not confusing you more,

    Tony
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Solarroofs.com system install

    Well OK, let's see if I can quantify the intended setup........

    First, adding plumbing to the existing plumbing when there is already a recirc line in place doesn't make sense and wouldn't be very simple in this house.

    Also, using the existing recirc means I can use the existing flue when I disconnect it from the existing water heater.

    Then there is the issue of the washing machine, guest bedrooms and the dishwasher that are all on the existing recirc system - they may need hot water at those times when the solar isn't up to it.

    And finally, there is no place to put this unit except by the existing water heater.

    n
  • Solar GuppySolar Guppy Solar Expert Posts: 1,959 ✭✭✭
    Re: Solarroofs.com system install

    How many collecter did you install? a low cost soultion, maybe to add more collectors to the solarroofs system you just installed. I had about 40sf that got the water into the 160's no problem with a 40 gallon tank in the summer

    Also, did you use the pipe insulation for the send and return lines to the collectors?
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Solarroofs.com system install

    Hi SG, the temperature of the stored water seems fine - adding another collector will only make the water usable (and hotter) on a marginal day at best, but won't do much for those cold rainy days when we still need hot water. It did cross my mind that another collector might be useful, but that doesn't solve my dilemma of being able to control the alternate method of efficiently heating the water with gas when it needs to be heated.

    The high density foam insulation that the system came with appears to be working fine - on both sides all the way to within an inch of the collectors.

    Many thanks,
    Nick
  • TelcoTelco Solar Expert Posts: 201 ✭✭✭✭✭
    Re: Solarroofs.com system install

    If you want usable hot water provided by the sun for a longer period, then one answer would be a larger collection system with storage. More collectors will let you collect more heat, and storage will last quite a while.

    If you have an area that you can devote about a 6ft cube (1 cubic ft is 6 gallons of water), or something along those lines, you could have a 1300 gallon storage area, and with this much water heated to 160 degrees in a well insulated box the water would stay pretty hot for several days with no input from the sun. A cheap method of building this would be sealed concrete blocks with a couple of inches of foam around them. You can either put the insulation on the outside or the inside depending on whether or not you want to use the concrete block's thermal mass to help keep the water hot. Be easier to build the box a little larger and insulate the inside. I've even seen pics of these boxes built from plywood and 2x4s, with a rubber bladder used to hold the water in.

    With something like this, it's likely you wouldn't need to mess about with a demand water heater unless you just wanted to.
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Solarroofs.com system install

    There are cold water recirc systems out there that use the cold water supply to return the hot water back to the tank. I'm no expert, but I surmise that you could still use a fractional hp pump, recirc the hot water through the cold, use the hydronic to preheat, and the Takagi to boost as needed.

    I still ascribe to the notion that heat the water with gas early when it will be over heated by the sun later is not very efficient. The bottom line is that the house, in toto, uses X BTUs a day. If you can get them all by the sun, and figure out how to manage them,, you win!

    Tony
Sign In or Register to comment.