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SolarInterested

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Reply with quote  #11 
gregkn73 thanks for your reply and the picture. Heating the soil in your covered and raised beds with water circulated from your storage 'tank' should get the most out of the stored heat.

Look like you've got quite the setup for a green house.

How large will your storage 'tank' be?



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Both temperature rise and airflow are integral to comparing hot air collectors

gregkn73

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Reply with quote  #12 
Greenhouse is 6m*2m, the storage insulated pod, will be 6*0.5*0.5 deep, if it is not big enough, I can make it deeper, but the other dimensions can not change.

So do you thing that this set up with car radiator is a lot better than an shcs?
SolarInterested

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Reply with quote  #13 
Just did a little Googling on SHCS to gain a bit of an understanding about the systems. I think they may be easier to engineer when building a new greenhouse from scratch but really tough to retrofit to an existing greenhouse. Lots of folks seem to like them but then the storage capacity of water is so much better.

Anyways, your plan looks to be a good fit for your situation. It looks to be similar to the system below except your tank will be in ground:
http://www.builditsolar.com/Projects/Sunspace/GreenhouseHX/GreenhouseHX.htm

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Both temperature rise and airflow are integral to comparing hot air collectors
JohnGuest

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Reply with quote  #14 
The heat capacity of water is great, transferring heat from the air into and out of the water is the tricky part. The heat transfer depends on the amount of air you can move through the radiator. If you cant move enough heat to keep pace with the incomng gain, the greenhouse will overheat.
Consider a fan running 645cfm (0.2-0.3 iwc) for an hour with air entering the radiator at 90F and exiting at 70F would heat the water by 1 deg F.
A well designed shcs will cool the air to the mass temperature with flowrates upto 25 greenhouse air volumes per hour. Diminishing returns set in at around 60 greenhouse air volumes per hour.
gregkn73

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Reply with quote  #15 
Quote:
Originally Posted by JohnGuest
The heat capacity of water is great, transferring heat from the air into and out of the water is the tricky part. The heat transfer depends on the amount of air you can move through the radiator. If you cant move enough heat to keep pace with the incomng gain, the greenhouse will overheat.
Consider a fan running 645cfm (0.2-0.3 iwc) for an hour with air entering the radiator at 90F and exiting at 70F would heat the water by 1 deg F.
A well designed shcs will cool the air to the mass temperature with flowrates upto 25 greenhouse air volumes per hour. Diminishing returns set in at around 60 greenhouse air volumes per hour.


That is exactly the kind of info I was searching. How effective is the heat transfer from air to water by the use of radiator. What you are saying is that I will need nearly 40% bigger fan with the radiator, to have the same results,as shcs=> increased operational costs....but I know the numbers of shcs fans are as you described! x10-40 of greenhouse volume is the fan capacity needed. But can I ask you, where did you find the numbers for the radiator fan? 645cfm for decreasing the air T from 90 to 70 F, and increase water T by only 1 F?
JohnGuest

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Reply with quote  #16 
The radiator will need to be sized to deliver the required performance. you`ll need to account for surface area, material used (copper, alu core). air and water flow rates, delta-T`s etc.etc.
In the example, if the radiator cools 38,700 cubic feet of air by 20F in one hour (in energy terms) it will have removed the equivalent btu required to heat 3300lbs of water by 1F. 
A 967w water heater running for one hour is another way of expressing the same amount of energy.
gregkn73

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Reply with quote  #17 
Quote:
Originally Posted by JohnGuest
The radiator will need to be sized to deliver the required performance. you`ll need to account for surface area, material used (copper, alu core). air and water flow rates, delta-T`s etc.etc.
In the example, if the radiator cools 38,700 cubic feet of air by 20F in one hour (in energy terms) it will have removed the equivalent btu required to heat 3300lbs of water by 1F. 
A 967w water heater running for one hour is another way of expressing the same amount of energy.


John I don't think the sizing is so complicated as you described. I will need a big enough radiator, and regulate only the fan speed to achieve the desired results. As far the cost of using the two methods,

I know that with shcs will need an *25 my greenhouse volume inline duct fun. In my case 6*2*3m = 36 cubic meter * 25 = 900m3/h fan. An 980m3/h inline duct fan needs 150W.

With car radiator and 1500lt underground insulated pod, the only reference I have as far operating cost is http://www.builditsolar.com/Projects/Sunspace/LowCostHtStorageNathan.pdf, with 60w*2 fans working only for 0.5h ,could lower his 10m3 greenhouse T over 10 C!

So with an shcs I estimate 8h/24h * 150w for fans
With car radiator 2.5h/24h *120w for fans + some negligible W for pumps. So if my maths are OK the car radiator method will be a lot more economic to use than shcs! Also it is a lot easier to construct.

So please specify how in your example , you calculate the numbers and why? Also since I can see that you have an shcs for 8 years now, what drive you construct one? The example I link above is from 2007, indicating car radiator method is simpler and more cost effective. I am very interested to read your opinion with specific numbers preferably. Thanks in advance.
JohnGuest

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Reply with quote  #18 
Assuming you have 530cfm running through a 2ft x 2ft radiator the air will have a 0.15 second window to transfer heat. Using the shcs as a yardstick, it takes around half a second to scrub 30F off the air. With 0.15 seconds (same flow, shorter tube) i wouldnt be expecting a 30F drop. The best you can do is  get the air leaving the radiator to match the water temperature entering the radiator while running the maximum air flow rate. If you have to reduce the airflow rate to do it, the radiator will need to be bigger
SolarInterested

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Reply with quote  #19 
colinmcc posted a link to an article about a solar hydronic 'root heater'

Whitehorse man's homemade 'root heater' is growing veggies faster, longer (link)

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Both temperature rise and airflow are integral to comparing hot air collectors
JohnGuest

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Reply with quote  #20 
I think a solar air "root heater" would be more efficient.
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