Improving Radiant Heating With Solar

[chibear]

I have a cabin <>60 miles North of Winnipeg. In preparation for my retirement I have added a basement and hydronic radiant floors throughout. The floors and domestic hot water are heated by a Rinnai 2532C propane boiler/water heater. This winter it will be run as installed.

In the spring I intend to begin preheating the both the DHW and radiant floors using solar panels (used&cheap, but in good condition) to heat a 1500 gal tank of water via a closed glycol loop with heat exchanging coils and running closed coils for DHW and radiant floors through this. The tank was made with a special resine to withstand 160 degree F temperatures without deforming. It will be surrounded with 12" of expanded polystyrene. I intend to also add a wood boiler (HS Tarm AD 24) to the tank heating system if the solar solution proves inadequate in the winter

I need now to find suppliers for the heat exchange coils & control system for the solar panel loop.

It will be interesting to see the savings provided by the solar addition.

 

[jasonweir]

try these guys,

http://www.radiantsolar.com/

[ghurd]

Dairy farmers and suppliers use and make a lot of different types and styles of heat exchangers. Competition keeps the prices reasonable for the high quality (pronounced "FDA Approved").

Worth a Google search.

G-

[chibear]

I like their solar loop control.....Thanks

[jimovonz]

I have put together my own solar radiant floor heating system. My heat exchangers are 100' coils of 3/4" soft copper (2x50') that you can get from any plumbing supply store. I made my own controller based on the picaxe micro, but controllers are readily available from any solar heating system retailer. I have heard of folk simply using an appropriately sized PV panel to drive the panel circulation pump - when the sun is out, the pump circulates water. I must say, your tank is quite large. I have a 500gal concrete tank that services my needs perfectly well. I have a 2800ft2 straw bale house. By my calculations you will be able to store approx 450kWh in this tank - enough to heat my house for approx 10 days! It would take your average 8'x4' panel over 4.5 days to heat a tank of this size from ground temp (15degC) to a suitable heating temp (22deg) here where I live. When sizing my system I made extensive use of the data you can find here: http://www.fieldlines.com/story/2004/10/6/164945/703

[chibear]

Thanks jimovonz, I did think about the 3/4" soft copper, but was hoping to find some flexible 1"  material to avoid too much drop in flow due to friction. I'm glad to see it works for you. I think it may be the cheapest workable option in the end. It was recommended that I use 2 4x8 panels for my purposes. Where are you located & how many panels are you using for your system?

[jimovonz]

The soft copper pipe I got was also available in 1" - although it was slightly more expensive per m2. It would be unusual for pressure drop to be an issue as the flow rate is so low, however if you are concerned, your heat exchanger will perform just as well if you split the two coils in half and run them in parallel. This will give you the same area for heat exchange with reduced back pressure. I use the equivalent of 4 4x8 panels which requires that I periodically use the wetback on the fire to boost temp in the middle of winter and that I cover two panels over summer (plan to add a swimming pool to utilise the heat at some later stage . I am in the North Island, New Zealand. If you follow the link in my last post you will find solar data specific to your region. Among other things it will tell you how much solar energy falls on a panel of a given orientation. You can count on your typical flat plate panel being 50% efficient (more at lower water temps, less at higher temps). Working out your heating requirements is a little more involved, but can be done using the data on this site also. If you add up the surface area of the wall, ceiling and floor types, you can estimate the R-values and work out the heat loss for given inside/outside temps. If you use the average daily outdoor temps for the coldest part of the year, you can work out your max daily heating requirement. You can also add in potential solar gain and heat input due to occupancy (approx 100w per adult). Don't forget to make an allowance for draw off for your household hot water if you plan to utilise your solar heat for this as well. 12" insulation for your tank is probably overkill - especially for such a large tank. Large tanks have a much lower volume/surface area ratio which means that they cool much more slowly. My tank is in the ground in a hole retained by 4x6 boards in an octagonal shape. There is a min 2" gap between the sides of the tank and the wall of the hole. Before I added insulation it lost approx 3 degC overnight (from 80 degC) during winter. I have added polyurethane foam (mixed up and poured directly into the hole) and now see much less than 1 degC drop over night (tho haven't been through winter yet...) Apart from the occasional fire during the coldest part of winter, my system works very well and provides all my hot water/heating needs. I am happy to share any info on how I have made it work. The entire system has been made on the cheap and is made from used parts. It has cost me in the region of NZ$1000 ($US 600) + a lot of my time.

[chibear]

Here are a couple of pictures of the installation before I insulated everything. At the upper LH corner is a flow switch that turns off the space heating system when domestic hot water is called for. Near it is a tempering valve that will be used if the Rinnai must ever be set above 140dF to accomodate the delta T of the radiant floor (unlikely according to the pros, but best to add it now). The gold pump activates the Rinnai; the red pump circulates the glycol mix through the heating system. The little box bottom center is the fluid-fluid heat exchanger. The Rinnai supplies 130d water. After 4 minutes running, the output at the heat exchanger is 115d. This was before I insulated everything. I expect better performance now that all the insulation is in place. Will be curious as to the performance when the temperature dips to -40 in January.

This picture shows the zone valves and basement manifold and my sloppy wiring (No matter how neat I try to be it never looks like the pros' work). The system works like this: zone thermostat calls for heat; zone valve opens; when zone valve opens an end switch is tripped; this activates a relay that turns on both pumps; the Rinnai detects the flow and turns itself on. Butta Boom Butta Bing!

[jimovonz]

Looks mighty fine to me! What did you end up with for your heat exchanger?

[chibear]

I'm going to go with copper tubing as you suggested. Apparently 1" flexible tubing is hard to come by here, at least the suppliers I've checked, so I'll probably go with 3/4" probably going with several shorter coils from a manifold so as not to lose pressure.

[chibear]

Problems with the Rinnai:

Got to the cottage on Christmas evening and found the Rinnai down and the temperature inside the cottage a balmy -12C. I estimate the unit was down around 24 hrs. The water was not shut down, but, when I redid the plumbing this summer, I used mainly PEX with only short pieces of copper. Add this to a lot of luck plus OT from our guardian angel and total damage was the loss of one faucet (whew!!!).

Rinnai seems to think the problem was in the intake/exhaust. We went through a week of -50C wind chill and the exhaust condensed, froze, and blocked the intake. They sent me a new intake/exhaust that extends the exhaust about 8 inches past the intake. The next cold snap will tell if this solution works or not. Otherwise the unit has performed really well, handling both domestic hot water and heat. Even though I have quadrupled the square footage I am heating, it looks now like I will only use around 33% more gas than the old system.

[chibear]

Update on Rinnai:

Another week of -40C+ wind chills. The Rinnai lasted around 48 hrs and then shut down. This time the installer looked at it and apparently it was ice crystals on the intake again and really very few to trip the sensor and shut down the machine. The new vent didn't do the trick. My thought is that some of the moist exhaust gasses are still being sucked into the cold intake and condensing & freezing. I am looking at ways to isolate the intake from the exhaust a little more.

[chibear]

Well, I tried isolating the exhaust from the intake with a drywall lean-to, cutting a small hole for the exhaust and leaving the intake inside (the sides were open for intake air. The ambient temperature dropped to -45C without wind chill and there was no frost around the intake; unfortunately the exhaust froze and I had to thaw it out with a plumbing torch. So much for that idea. Next weekend I'm going to try wrapping the intake pipe in metal and applying heat tape on a timer and see how that works.

[chibear]

Final fix:

I consulted with the vendor and we decided my best option was to drill a hole in the intake inside the house. This reduces the velocity of the intake gasses going through the outside intake and also raises their temperature, so should address both problems. I also added another 8' of intake pipe (inside) with a damper on the end for some control and a make up air intake elsewhere in the room. It was -31C this morning and no frost on the intake. The only thing left to do is to experiment to find the ideal setting for the damper on the indoor intake.

[chibear]

It looks like the heating season is finally drawing to a close. Passive solar gain alone keeps the buildings over 15C when we are not there. A single wood fire does the rest when we are.

Total propane usage for 04-05, includes space heating, domestic hot water, gas range, BBQ and mosquito magnet: 3574 litres

Around 2 cords of mixed firewood (birch, balsam, oak & poplar)were burned in our stoves

This was an extremely cold winter for our area. December and January set records for all time coldest months & in January the mercury dipped to -45C not including wind chill: 2C from the all time cold temperature ever recorded in Manitoba