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Forum Index : Solar : Deciding if I should build this solar heater
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| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The picture at the lower right of a pumped water solar system is exactly what you want. Connect your air blower to the "pump" connections, terminals I and 3 in series with your air blower. Low temperature sensor T1 will be your "room" temperature sensor. High temperature sensor T2 will be your "tube" temperature sensor. Set Ld to lowest diff temp where you want your blower to turn off (<5C ?) Set Hd to highest diff temp where there is sufficient heat worth harvesting (>15C ?) You can then set the display to monitor the current differential temperature "d" or the tube temperature "CA2" or room temperature "CA1". At least that is my interpretation of what it does...... Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Thanks very much Tony, I need to get out and try it. I don't know why I wasn't able to work it out ... it all becomes a jumble when I try to think it through.  Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
You are not alone Roger. I hate these things you have to program before they work. Where there are multiple layer menus, and complicated sequences of key strokes, and where the instructions are vague, indecipherable if not self contradicting. Try first connecting it up on the kitchen table in reasonable comfort with a cup of coffee, with an ohm meter across contacts 1 and 3. It should be possible to get it switching on and off from just body heat by holding onto one or the other temperature sensor. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
The controller will certainly add a lot of Functionality to the system. Give Roger the ability to actually set the temps he wants the house to be. With a motorised Diverter or what ever they are called in the air con game, It would also be easy with a little more control to send the heat once they house has reached Temp to a Dump load in effect like storage, a green house or for Fruit drying etc. Roger are you incorporating any shutoff dampers in the system? When the Diesel heater was not working we had a lot of winds here. There was surprising Draft blowing through the heater which was counter productive to heating when the outside air was 3o. It may be possible that the system could leak cold air at night or the warm air in the house could backflow out and bring drafts in. Smmer it may be the Tubes create a Thermo syphon that wants to suck the cool air up and out the house pulling hot air in. No idea if this could be a legitimate problem but may be worth doing the mental arithmetic now so you can design in a solution if need be rather than have to make one fit later on? Of course could be as simple as putting a pipe cap on the outlet or my cunning and highly technical solution of stuffing a tea towel in the opening. :-) If you are going to have the system automated with the controller, a servo motor operated damper in conjunction may be a better option however. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The differential temperature controller will pump hot air into the house whenever the tubes are hotter than the room by some minimum amount. When the tubes are cooler, the blower will stop. Its a one way heat flow without any control of room temperature, but it can never blow cold air. It will just cycle on and off adding extra heat when its available, and stopping when heating is not available. The room temperature should ratchet upwards. For control of room temperature, Roger will need to add a room thermostat to override control of the blower when the room is up to the desired temperature. Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
It's funny that you should ask that right now ... I've been researching them over the last couple days as I definitely do want to use some. As much because I want to send air to two different areas and I wanted to be able to shut off one or the other ... or maybe both ... to prevent exactly what you were talking about in your post. Been looking on ebay and aliexpress etc ... but found some very similarly priced ones at Rheem Plumbing here in Aust .. and we've got a branch a km away. Only thing is that these are a heavy black plastic assembly ... so may feel more comfortable with a metal bodied device, considering the possible heat levels, and hot plastic smells. Yeah, I've certainly noticed the cold wafting out the outlet at night time occasionally, though I never got around to stuffing a towel in it ... had certainly considered it ... I just pull down the blind and turn a blind eye. Bit lazy like that. Well I did as you suggested, and played with the device. Almost felt like I was getting the concept, but it still alludes me. Bit like my 60 y/o tractor ... a couple of pops and bangs and a cloud of black smoke ... but not starting yet! I need to substitute the sensors for a couple of 'calibrated' pots ... and fit a 12v light globe on the output relay ... then I reckon I'll get a grasp. ATM I still keep coming back to thinking I need an 'absolute' temperature sensor in the system somewhere ... but I'll work it out.  I'm still some way away from needing a sensor to stop the room getting too hot ... at least for my wife ... she'd be happy to see the paint peeling off the walls. Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Its basically operates like a temperature diode. When one sensor is hotter than the other, the blower starts up. When the temperature difference is zero or almost zero, (or in the wrong direction) the blower stops. Absolute temperatures do not matter, its the temperature difference between the two sensors that causes the blower to start or stop. So as everything heats up throughout the day it still works normally. You can buy kitchen or laundry exhaust fans fitted with automatic shutters. When the fan is de powered the shutter closes, keeping out the outside cold (or heat). Here is one example from Bunnings, I have not actually looked at one of these, but I believe its the right type of thing: https://www.bunnings.com.au/blauberg-150mm-white-auto-wall-ceiling-exhaust-fan-with-automatic-shutters_p4420512 Now what you could possibly do is hook up more than one of these to your system, each with its own individual room thermostat. When a particular room has reached an optimum temperature that particular fan no longer starts up when heat is available, but other rooms may still require heat. These are all exhaust fans, but the motor rotation is easy to change with a bit of mechanical disassembly and reassembly. Not sure what opens and closes the shutters, but hopefully it may be by an electrical solenoid. Anyhow, it should be possible to duct heat to more than one place, even to select some kind of heating priority based on time of day for example. A whole range of possibilities open up. But the differential controller will indicate when heat is available, and when it is not. That will become the master controller for the whole system. Cheers, Tony. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The motors in these exhaust fans are of the shaded pole type, with a single 230v winding. Its not possible to reverse the motor electrically.  What needs to be done is the rotor needs to be removed by taking out two long bolts, and turned around, so drive shaft sticks out of the back instead of the front. Then if the whole motor is turned around and reinstalled in the housing, the fan will turn in the opposite direction and blow air instead of extract air. Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
I think that's where my sticking point is ... it's not unusual for the tubes temperature to be sitting at say 35 degrees (a very useful temperature) ... and for the outlet temperature to be a degree or two higher. And even if the outlet is a degree lower ... I still don't want the fan to turn off. In fact, I only ever want the fan to turn off if its temperature goes below about 25 or 26 degrees. As you can see, I still don't understand the controller principle yet ... I need to do the next step with the pots and lights! Sorry, slow learner here. I hadn't thought about that type of exhaust fan ... it is certainly a possibility. And I don't know about your example ... but I have seen old fashioned ones like that, that use a larger vane near the fan to flip the vents open with air pressure ... and when the fan stops, spring pressure pulls them shut again. I'll have to go for a wander at Bunnos after the current lockdown finishes. At this stage it's a bit hard to see the temperature getting too high ... but I guess we've almost reached that stage with the existing device a few times ... so I need to plan ahead. For the new one, I have to admit I can see value in having a more complex control system so that I can get to learn how it is performing more easily ... where perhaps I'll have temp sensors all over the place, within the heater and around the house ... and I can see at a glance what's happening at a central point ... and program in the control from there. Certainly it will have to include solar panels to run DC fans ... no point doing all this and still having to rely on the mains. I didn't realise you can reverse that style of motor, very handy to know. I probably don't need them here ... but I do have a heap I saved from wrecked microwaves. Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
If the room is only at say 5 degrees first thing in the morning, you want the fan to come on whenever the tubes are usefully hotter than the room is at 5 degrees. Maybe at 20 degree tube temperature or more. If the room is up to say 20 degrees, you want the fan to come on whenever the tubes are perhaps at 35 degrees or more. Its not absolute temperature that controls things but the DIFFERENCE of how much hotter the tubes are than the room. If you set your differential controller to come on at 15 degrees positive difference, that is what it will do. You can set the fan turn off point lower at perhaps 5 degrees positive difference (still hotter) than room temperature, so it can then never blow cold air. So when its freezing cold in the morning, the system starts up much earlier. But as the house heats up, the temperature controller follows that up. Cheers, Tony. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
O/k here is an example. Set Ld (low differential) to 5 Celsius Set Hd (high differential) to 15 Celsius. First thing in the morning, room temperature only 5 degrees. Fan starts up at 20 Celsius (5+15) tube temperature, turns off at 10 Celsius (5+5) tube temperature. Mid morning room temperature rises to 17 degrees. Fan starts up at 32 degrees (17+15) tube temperature, turns off at 22 Celsius (17+5) tube temperature. Mid Day room temperature 22 Celsius. Fan starts up at 37 Celsius (22+15) tube temperature, turns off at 27 Celsius (22+5) Mid afternoon room up to 29 Celsius Fan starts at 44 Celsius (29+15) tube temperature, turns off at 34 Celsius (29+5) Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
I had a light bulb moment last night (I hope). I've been trying to understand this differential controller with the view to using one sensor inside the tubes ... and the other sensor in the hot air outlet ... duh! I gather I should have the second sensor picking up the room temperature! Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Yes indeed !!!!! Hot sensor in the tube, cold sensor in the house. The blower then starts when the tubes are hotter than the house, and stop when there is no worthwhile heat to transfer. Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Told you I can be a bit thick at times. Thanks for your perserverance.  Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Once this is all set up and going, I think you will find it will make a remarkable difference, especially on very marginal cloudy days. Cheers, Tony. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Hint... Put the cold sensor in the coldest part of the room, in other words, well away from where the hot air enters the room. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I have gone a little against that with my diesel heater. I put the sensor bedside but distanced from the output. The heater blows pretty well and I believe the hot air shoots well into the middle of the room. I think having the sensor beside the outlet is pretty much the same as having it on the other side of the room because if anything, I am of the opinion that the output air may cause a sort of venturi airflow that pulls air in from around it which would all be cold. Bit like I can stand right beside a high speed flame shooting out of an Orifice and there is no real heat apart from the radiant which is not present in a gas flow like this. The sensor on the heater seems pretty questionable in it's readings so in effect I use the thermo gun from a Diagonal wall and the floor. The main room seems pretty consistent anyway. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I know what you mean Dave, and you are quite right. It all comes under "final fine tuning". Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Okay, so I've finally just fitted this controller ... and I set it how you suggested Tony ... with the Ld at 5 degrees and the Hd at 15 degrees. You've been spot on with everything else so far, so I need to listen for a change. Yesterday was our coldest, darkest, wettest day so far this winter ... so I didn't get anything from it. The highest I saw in the tubes was 24 or so ... but turning on the fan still had the output at around 15 ... so switched straight off. This morning on the other hand is back to a nice sunny day. By the time I wired it up it was 11:30 and the tubes were up over 90 degrees ... actually over 110 ... because even the differential controller is showing an error on the tubes temp sensor and its maximum reading is 110. I've put the fan onto high speed because I (hopefully) won't have to keep an eye on it myself any more ... and let the control do its job. When I first fired it up ... the outlet went up to 60 degrees within seconds and as high as 88 degrees inside a minute. After 15 mins or so ... the tubes had dropped to 61 and the output 50. I suspect the output will drop to 30-35 if the sun stays out ... or nose dive if it gets cloudy. 20 mins later ... Well, I just had another look and cloud has come over and tubes have dropped to around 30 ... and the outlet is around 28. I realised that because the room is still only 16 degrees ... 5 degrees on the controller means that it will keep pumping until the tubes are down to 21. That is too cold, coz the outlet will be a degree or two below that ... maybe 19. So I reset the Ld to 10 degrees ... and I watched while the tubes dropped to 26.3 (room 26.4) ... and the fan switched off!!! Now I can wait until the cloud moves, and the tubes get back up to around 31 when the fan should come back on. Haha ... and while I'm typing this I realise the fan did come back on already. I went and had a look ... and saw that the temp was dropping again. Amazing, this is working exactly like it's supposed to. When it switched off ... the outlet was pumping at 24.8. May be a couple degrees too cool ... but getting close already. Just needs fine tuning like you said Tony. I know, I know, oh ye of little faith!  It's done a couple cycles already ... I can hear it from here. Amazing. Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Fantastic progress there Roger, it might need a little tweaking still, but basically sounds like you have a goer. Cheers, Tony. |
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