passive solar dump tank

Users who are viewing this thread

Stalker

New Member
Messages
2
Reaction score
0
Points
0
Okay I am designing a passive solar heater. I hope to have it up and running by next winter. here is my question, for now. I'm sure more will come.

I want to install a tank that the radiators will dump into when the system first starts. This will also serve as a place for any trapped air to collect, and to keep the water lines filled.

Here is my plan, go ahead shoot it down. I am basically building a green house that will house several in line floor board radiators. You know the copper pipes with aluminum fins. THese will heat up and then circulate hot water, into two hot water heater tanks, these will also be inclosed in the green house under the radiator/solar collectors. THe hot water heaters will run in series, the second one will supply water to the forced hot water system inside the house.

I don't see this system ever getting hot enough, that steam becomes a problem. SO if I put my dump tank at the top of the system, so it will serve to keep the cold water sitting in the house pipes, from directly cooling the water in the system, will it effect the weight of the water being pumped through the system?

I plan on using a fairly inefficient pump to save on electricity. So water weight is a concern.

In case you are wondering. This will be a secondary system that will only heat the bottom floor of my house which is below ground.

Thanks for reading this
Stalker
 

Scuba_Dave

Extreme DIY Homeowner
Messages
868
Reaction score
2
Points
0
Location
South of Boston, MA
Website
holidaves.com
Where are you located?

My greenhouse was up to 105 the other day, just about 70 outside. I was bumming that I didn't have the solar heater built yet

GH09web.jpg


I'm building a can-0-later air heating system
Air heats up faster, but cools off faster
No mechanical moving parts

The greenhouse cost me $30 to build
The solar heater will be about the same
This is one someone else built
The air coming out the top in the winter is 85.3

slidingdooroutsidepanel07m.jpg


panel06m.jpg
 

Stalker

New Member
Messages
2
Reaction score
0
Points
0
I live in Northern Virginia, Just south of Washington D.C. It gets pretty cold here so I want to use forced hot water instead of air to protect from chilling at night. IS that a problem for you? It seems to me that at night, the device in the picture would produce cold air.
 

Scuba_Dave

Extreme DIY Homeowner
Messages
868
Reaction score
2
Points
0
Location
South of Boston, MA
Website
holidaves.com
Actually the doors get shut when it gets colder outside
The person who built it has someone (wife) who is home during the day.

Most solar systems properly built will work
Its just a matter of finding the right design/setup

SO if I put my dump tank at the top of the system, so it will serve to keep the cold water sitting in the house pipes, from directly cooling the water in the system, will it effect the weight of the water being pumped through the system?

I'm not sure what you mean by this?
Are you concerned about the weight of the system & supporting it? The water stored above will put pressure thru the pipes below, helping thru-put. But that is then offset by the force required to pump the water back to the tank
 

Master Plumber Mark

Sensitivity trainer and plumber of mens souls
Messages
5,533
Reaction score
354
Points
83
Location
indianapolis indiana - land of the free, home of
Website
www.weilhammerplumbing.com
heated greenhouse??

I like the passive solar system and the pics... that will certainly partially
heat up the house during the days
.


I dont know how well your idea is , as far as getting something out of the system during the day with sun , it
will probably heat the lower level...very well

at night it will probably fizzle out pretty quickly, unless
you have massive heat and massive storage for the heat
you have collected during the day... you might only be able to partially keep the lower level heated before the tanks cool off. its all depending on the size of your storage tanks.

I suppose this is gonig to be some sort of drain down
panel sysetm>>
and the green house is going to be heated during the winter to keep all the pipes and from freezeing
during periods of cloudy days??
 

Scuba_Dave

Extreme DIY Homeowner
Messages
868
Reaction score
2
Points
0
Location
South of Boston, MA
Website
holidaves.com
One of the shows on TV went thru a solar hot water installation
The storage tank was around 1200 gallons & was in an insulated space

My greenhouse has been up over 80 since before 9a
Right now it is 85
So since before 9a I could have warm air flowing into the house
If I had to wait for water to warm up it would be longer

But it depends upon your storage capacity
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Okay I am designing a passive solar heater. I hope to have it up and running by next winter. here is my question, for now. I'm sure more will come.

I want to install a tank that the radiators will dump into when the system first starts. This will also serve as a place for any trapped air to collect, and to keep the water lines filled.

Here is my plan, go ahead shoot it down. I am basically building a green house that will house several in line floor board radiators. You know the copper pipes with aluminum fins. THese will heat up and then circulate hot water, into two hot water heater tanks, these will also be inclosed in the green house under the radiator/solar collectors. THe hot water heaters will run in series, the second one will supply water to the forced hot water system inside the house.

I don't see this system ever getting hot enough, that steam becomes a problem. SO if I put my dump tank at the top of the system, so it will serve to keep the cold water sitting in the house pipes, from directly cooling the water in the system, will it effect the weight of the water being pumped through the system?

I plan on using a fairly inefficient pump to save on electricity. So water weight is a concern.

In case you are wondering. This will be a secondary system that will only heat the bottom floor of my house which is below ground.

Thanks for reading this
Stalker

If I'm understanding you correctly, you intend to use fin-tube baseboard as air-to-water heat exchangers heating the water with the solar-warmed greenhouse air convectively, then pumping the tepid water into (un-fueled) hot water heaters tanks for thermal storage to be drawn on by the indoor heating radiation?

The efficiency of such a system will be somewhere between extremely poor and downright atrocious. Getting any heat transfer from the air into the water via fin-tube at any reasonble rate requires the greenhouse room air to be at least 50F above the temperature of the water. Even if your indoor radiation is a radiant floor, you need water temps of at least 30F above the room temp to support a "real" heat load. So... that means if you want to keep the room at 65F your stored-water temps need to be 95F or higher, and to get those temps into your fin-tube at any reasonable transfer rate your greenhouse room-air would need to be 145F for several hours.

The weight of the water is inconsequential to your pump- the HEAD of the system (height it needs to pump to plus piping friction) is. The weight of the stored water IS consequential to your ability to store heat at low temps. A BTU is the amount of heat it takes to raise a pound of water one F degree, and you'll be needing to store thousands (tens of thousands really) of BTUs to have a "useful" amount of stored energy to dump into the home's heating system.

If you only have two 40-gallon hot water heater tanks for storage, that's 80 gallons @8.34/lbs/gallon, or 665lbs. To be able to "keep up" with a typical overnight heat load when it's 50F out (not exactly cold), you'll need on the order 10,000BTUs/hr for say, 8 hours which is 80,000BTUS (about what you get out of burning 100ccf or 1 therm in natural gas in an 80% efficient furnace, or about 3/4 gallon of heating oil in a similar appliance).

That means your storage temps need to be 80,000BTUS/665lbs= 120F above your minimum indoor radiation requirements. (lotsa luck on that too)

But if you had 800 gallons (say, well-insulated lined septic-tank sized thing buried under your green house) you'd only need to store water at 12F above your minimum radiation temp to store that much overnight heat- much more manageable.

Low temp solar can work, but you need lots of storage, and lots of reasonably efficient direct-sunlight collector area (not a few square feet fin-tube heat exchanger in the greenhouse.) If you want to use the greenhouse for space-heating your home you'll get 100-fold better efficiency out if it by circulating the air between the house and greenhouse with well-sealed ducts and a fan/blower- forget about storage.

If you still want to use water and heat storage- use a buried well-insulated tank (a big 'un), and use some of those 2x20' (or 4x20') plastic swimming-pool solar heaters mounted vertically a few inches away from the greenhouse glazing along the inside of the lower part of the S-face of greenhouse wall. Then operate the pump using a differential-thermostat to heat up the tank whenever the heaters are warmer than the tank water. For freeze control in the greenhouse, setting up the pump to respond to an air-temp thermostat makes the pool heaters work as a low-temp heating radiator inside the greenhouse.

To max out the efficiency of such a system it's best if you allow/encourage the water in the storage tank to stratify, drawing the colder water from the bottom of the tank into your collector panels, and dump the hot water coming out of the panels laterally (not straight down) at the top. (you could use heat exchangers inside the tank and get even better performance, but I'm assuming we're not going there.) The pump to the inside-the-house heating system needs to be a separate pump, and it needs to draw from the top of the tank, with it's return dumping into the bottom via a dip-tube. (The opposite of your collector panels)

If you're now thoroughly disillusioned (educated?) and want to settle for moderating the temps & freeze-protect the greenhouse, you can do a lot with high-mass completely passive thermal storage: Dig the floor down a foot or so, insulate the-dug out area with 2" of XPS, and pour yourself a small "swiming pool" with of reinforced concrete with an EPDM plastic liner. Fill it with 1" screenings (round stones) with some lawn walkway pavers added where you need to walk, and fill with water up to just below the tops of the screenings. The stone doesn't have as much thermal mass as the water, but it's still considerable, and a water-filled foot deep collection of stone is about an order of magnitude more thermal mass than a 2" concrete slab.

For a whole bunch of low-budget and reasonbaly efficient DIY solar heating ideas, dig around on the build-it-solar site (there's quite a bit of relevant design info there.)

http://www.builditsolar.com

If you're going to be using hot water for space heating, read up on hydronic & radiant heating systems too.
 

Master Plumber Mark

Sensitivity trainer and plumber of mens souls
Messages
5,533
Reaction score
354
Points
83
Location
indianapolis indiana - land of the free, home of
Website
www.weilhammerplumbing.com
Dana, you have the best ideas so far......

I totally agree with your ideas Dana..

Storage is the key issue with any hydronic
heating system.

here is my dream solar system...

but not totally passive .......



If I had a the time and money, I would dig a hole somewhere in the yard and near the house, then install a large septic tank and insualte the sides of it with about 6 inches of styrofoam insuation, also you need to get it near where the panels would need to go..


this tank would hold about 2000 --3000 gallons of extremely hot water that some solar panels would be constantly heating, ...... this should give you a huge reserve to get through perhaps a few days without the sun...


this extremely hot water in the tank would be pumped into your forced air hvac system when ever the furnace would come on and pump through a heat exchanger in the phlenum. This basically can and will heat your home... very well indeed...


also you can put 600 foot of 3/4 pex down in that hot tank and use it to pre-heat the water heater.... no pump required


these solar panels work with glycol with a
100 foot copper coil for a heat exchanger sunk deep down in that water tank.... this can and will literally heat that tank as hot as hell during the day
I have literlaly seen one steaming hot before when I worked on one...



this system would work with just 2 simple pumps,
one for the soalr system, and one for when the furance comes on and
pumps the heat into the house.through the heat exchanger.
.... and just a small solar controller box..for the heat sensors....



I think this system is soooo sweet......









just another idea ...
 

Master Plumber Mark

Sensitivity trainer and plumber of mens souls
Messages
5,533
Reaction score
354
Points
83
Location
indianapolis indiana - land of the free, home of
Website
www.weilhammerplumbing.com
I dont know

Makes sense, & why on the TV show the Mfg was installing a 1200g storage tank


I dont know, but I just figure the bigger
the better ,,,,, and if you are going to bury a
bone , it might as well be a big one..
you certainly dont want to dig it up if it is too small..


perhaps I am wrong in my
ideas about a 2-3000 gallon tank...

I am thinking of storage and a massive lot of reserve..

the only down side I could see to it would be having
to heat all the water to 175....from an average ground temp of 55.

and perhaps it would take an extra panel?

this is all just best guessing ,

someone would have to run numbers....
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Don't guess- do the math. BTUs in must equal BTUs out- (it always does, eh? ;-) )

Calculate (or measure) your heat load...

...standby losses...

...average solar irradiation...

...calculate the collection efficiencies (based on average air & required design-day water temps)...

THEN you have a shot at determining the amount of panel area & thermal storage you need (and it will be an iterative process to find the right balance.)

You'll spend the money more appropriately/effectively that way. Hackin' usually just blows the budget for negligible gain.

First rule of solar:

REDUCE THE HEAT LOADS TO THE ABSOLUTE MINIMUM PRACTICAL.

Which means in 5000+ heating degree-day climates, if you don't have clear-wall R-values over R25 (over R35 is even better, if more economical in new-construction than as retrofit), you need to get serious about spending the money on insulation first, even if it means stripping the siding and adding 2-3" of unfaced iso-board under a new layer of permeable-sheathing (GP Stedi-R or Huber ZipSystem). R50+ (R70+ better) roofs too, even if it means spraying 5-12" of half-pound foam beween the rafters and sealing the vents + 3-6" of unfaced iso + nailer-layer over the roof deck to get there.

Otherwise the size & cost of the solar panels & storage necessary to handle the bulk of the load will be ENORMOUS.

Second rule of solar:

DESIGN THE SYSTEM TO OPERATE AT THE LOWEST TEMPERATURE POSSIBLE.

The efficiency of the collectors (panels OR evacuated tubes) drops dramatically with increasing delta-T between the outdoor ambient and collector water temp. (The colder it is outside, the greater the losses out of the collector, and the hotter the collector, the greater the loss.) The amount of collector area you need to achieve 175F stored water temps can easily be more than twice what it takes to achieve 120F stored water temps. See: http://www.viridiansolar.co.uk/Assets/Images/Technical/Solar panel efficiency curve.jpg And the standby heat loss out of the TANK will nearly double at 175F vs. 120F storage temps too. If you need 175F water to deliver the heat in winter, better buy stock in a copper mine, 'cuz that's gonna be a LOT of panel (running at pathetic sub-30% efficiencies when you need it the most.)

The whole point of going with large and very well insulated storage tanks is to be able to store significant amounts of heat a relatively low temperatures to keep both the collector efficiency up, and the standby losses low. More storage IS always better, for this very reason (up to some economic point where it's cheaper to buy another panel. More storage volume is usually comparatively cheap, but never free.)

In order to be able to heat your house with low temp water you need more radiation than the typical hydronic system (most are set up only with sufficient radiation to deliver "design day" heat with 160-180F water.) With a low loss R25+ wall/R50+ roof house radiant floors/panel radiators can usually deliver the heat with 100-120F water, but if you have sufficient wall length you can often get that out of fin-tube baseboard as well.

There's a reason why most older homes aren't very suitable for solar heating retrofit- they're way too leaky and under-insulated. From a cost/benefit point of view it can't make sense. (Solar domestic hot water- sure, but not solar space heating.) But there is often GREAT payback in older homes to doing some serious air-sealing and insulation upgrades.

It's easy to fall in love with the concept of solar (the fuel is free, right?), but when you do the math, it's boring old INSULATION that does the heavy lifting to enable effective solar. Only with sufficiently low heat loads from higher insulation and tighter construction will the rest is easy (or affordable.)

Before you spend ANY money on solar heating, get a serious full-on energy analysis on the place, including blower door testing and infra-red imaging to find & fix all the insulation gaps, thermal bridging/bypassing and air leaks. But even before you even do that, insulate your foundation (to 2x code or more), seal & insulate your bandjoists & sills, and replace your exterior doors with insulated versions. You may end up replacing or retrofitting a lot of glazing too (and PLEASE rip out and foam-insulate or dense-pack cellulose into the cavities for sash-weights on old-skool double-hung windows, even if you keep the sashes & storms for sentimental/cost reasons.)

The first-rule of solar really is a RULE. If you want to be effective you need to be cost-effective.

If you're burning over 1000 therms (=100,000cf or 100 decatherms) of natural gas, or over 800 gallons of heating-oil/year on heat + hot water you're likely to get far more bang-for-buck (measured in less fuel burned) out of upgrading the building envelope &/or higher-efficiency heating/HW systems than any solar inputs. If you're burning less than 500 therms/400 gallons you can THINK about retrofitting solar as primary heat if you live in an area with decent amounts of heating-season sun. (Sunny Salt Lake City, yes, foggy-dew Vancouver B.C. probably not.)
 

Bill Arden

Computer Programmer
Messages
584
Reaction score
0
Points
0
Location
MN, USA
Website
www.billarden.com
I've looked into making a system here (12,000 heating degree days, .6 cloud factor, -40F)

But in the end I decided to focus on insulation upgrades and a ground source heat pump.

I may return to solar, but here is how I would do it.

1. Concentrated collectors. Either toughs, dishes, or possibly even helostats and a power tower. The 3 foot by 8 foot solar trough that these other guys made was able to reach temperatures of 400F(without water) and could produce quite a lot of BTU's even when it was -30F outside.

2. Paraffin wax storage. I calculated that I could heat my entire house for a day using 250 gallons of Paraffin wax. The wax would melt around 110F and would produce 85F water to heat the house.

3. In floor Hydronic heating.

4. Alternate heat source.

The math showed that I could produce enough heat to reduce my heating bill by %41, however I determined that a ground source heat pump(open loop) and more insulation would cost less and possibly reduce my heating costs even more.
 

Bill Arden

Computer Programmer
Messages
584
Reaction score
0
Points
0
Location
MN, USA
Website
www.billarden.com
>.6 cloud factor
Please define.

Cloud factor is the ratio of the average insolation to peak insolation averaged over a period of a month at a specific location.

In other words it's a percentage meaning that it's Cloudy 60% of the time.
If I remember correctly I picked the January number.

Given the cloud factor we figure that we would only be able to heat a house 40% of the time even with parifin wax thermal storage for nighttime.


http://www.apricus.com/html/insolation_levels_usa.htm
 

Thatguy

Homeowner
Messages
1,454
Reaction score
3
Points
0
Location
MD
>.6 cloud factor


Cloud factor is the ratio of the average insolation to peak insolation averaged over a period of a month at a specific location.

In other words it's a percentage meaning that it's Cloudy 60% of the time.
If I remember correctly I picked the January number.

Given the cloud factor we figure that we would only be able to heat a house 40% of the time even with parifin wax thermal storage for nighttime.


http://www.apricus.com/html/insolation_levels_usa.htm
Don't you still need percentiles on continuous days of cloud cover to determine max heat storage capacity?
E.g., 1% chance of 10 continuous days of cloud cover, 10% chance of 3 days, 20% of 2 days, etc.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks