Heating Help

Yep, a 12 hour and few minute day on the summer solstice could find Cape Girardeau somewhere in Equador South America! Length of day here on June 21 is 14 hours, 44 minutes. Boulder, CO (close to the latitude from the other chart) has a day length of 15 hours, 1 minute on June 21. Only 17 minutes or about 2% longer.

Sorry--made those LOD figures inclusive so they're probably about 1 minute shorter...

I've definitely done the trigonometry to determine the area of the "shadow" to include actual sun elevation depending on day-of-year and time-of-day. The first and last two hours of insolation are usually so low that I just forget about them as there's not even enough energy to overcome the transmission loss. When the sun is lower in angle than the collector I re-calculate as if the collector were ideally oriented and then apply the vertical incident angle modifier based on the actual difference in angles. The nature of the insolation data [seems] to be self-compensating for the horizontal incident angle as I'm not tracking the panels left and right. Still haven't heard from the MO dept. of agriculture. Will write them again.

Is that like my

FLUX capacitor powered Delorean at all. You engineer guys make my head hurt. great info though I am considering some solar panels myself to experiment with for my radiant. I'll keep reading when my headache goes away. To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

If you look carefully you'll notice that from October through April there's a general delay of about 2 solar days between Swampeast MO and NJ that would [seem] to correspond very closely with the general movement of weather systems. Then notice the nearly polar opposites around the beginning of April and the beginning of August. Nor'easters while high pressure is building here? Between April and August notice how the general 2 solar day time lag is nowhere near as regular. This is when a gigantic high pressure "dome" typically builds centered right above Swampeast MO. This "dome" steers weather systems around Swampeast MO--at it's height a "ring of fire" occurs all around us. The air goes virtually stagnant, humidity builds and the sky is in a nearly perpetual haze of ugly grey. This is complete contrast from October - April when our clear days generally have beautiful blue sky. Perhaps I'm reaching here, but it sure looks to me like "general" atmospheric conditions can have a significant impact on solar energy received on the ground--much more than can be explained by the difference in length of day between these two latitudes.

adjustable collector tilt

Mike, consider installing a collector mount that you can tilt it, not side to side every day, but up and down as the seasons change. I have my collectors mounted fixed at about 65 degrees to capture the maximum winter sun, for heating, but with the sun directly overhead in the summer, I collect way less energy than I should be. If I could tilt my collectors to about 45 degrees in the fall and spring I think I could use it for heating a lot more. The steep winter tilt also keeps the snow off the tubes. If you are going away for vacation you could tilt the collector away from the sun, and you might be able to run home before a hailstorm and tilt your collector down. Bob Gagnon To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Mike,

have you looked into the retscreen resources? IIRC, their excel-based tools will do everything you're looking for...

Viessmann solar

Mike Here, this is out of the Viessmann solar design manual. I think this will help you. Viessmann really strives on education which comes lots of research. Jeffrey

Viessmann Solar!

Here is out of the Viessmann solar design manual. I think this will help you. Jeffrey

el sol

> Presuming that those insolation values _I_are_/I_
> as collected on _B_flat earth_/B_...
>
> Here's my
> _I_area specific_/I_ theory:
>
> Sunny winter days
> around here tend to be clear--_I_glaringly_/I_
> clear. Summer days however are rarely
> clear--there is a nearly perpetual haze of
> humidity.
>
> This sets up a situation somewhat
> contradictory to the conventional wisdom of "you
> have the least when you need it the most". The
> most available solar energy [seems] to be
> available when I need it the most.
>
> While the
> most may be available then, a BIG part of the
> solar efficiency equation kicks in--difference in
> temperature between the air around the collectors
> and the fluid running through them. While the
> most may be avilable, you're loosing the most due
> to temperature difference--since, after all, it's
> cold in winter....
>
> That's where I'm trying to
> use the solar energy to its best use regardless
> of the time of year. DHW preheat--I notice VERY
> often now that "preheat" is used instead of full
> domestic hot water heating--is not going to be
> the most efficient use in my system! DHW load is
> typically low during mid-day with the only
> exception being laundry day. With no DHW going
> out, you're not "pre-heating" you're
> HEATING!
>
> When AT LEAST 25% of my heating days
> (say from mid-October - mid-march) can be
> satisfied with no more than 85F supply with a
> return at or near ambient indoor temp it sure
> seems to me that the best use of the solar is for
> space heating. The clincher is that I get decent
> passive solar gain such that my actual heat loss
> _I_might_/I_ be 40% of that expected via Manual-J
> on a sunny day when the mid-day temp exceeds 38F
> or so.

Mike... re: the install directions

That link to a PDF that I posted up above shows how to set up a very high end model like they would use in any professional meteorological environment. Those puppies are leveled perfectly flat! The sensor is in a small clear dome. That said, you'd have to look at how it senses within the device. It is capturing the intensity in that little dome and expressing it as energy/m².

I'll write the MO Department of Agriculture to find out what they're using. Considering this is really related to growing row crops, it sure seems logical to me that it's the actual energy received by a square meter of flat earth. Perhaps I'm naive but if you wanted to measure available solar radiation flat on the ground wouldn't it require little more than a simple device mounted perfectly flat that converts sunlight to electricity? Why would you want a hemispherical measuring device unless you were trying to measure insolation other than as received flat on the ground?

"Develop your own criteria and measurement methods." That's EXACTLY what I'm trying to do. I'll do my best but it just seems odd that I can't find anything to make it MUCH easier. Then when I do come up with something I'll be savaged for it being merely site specific, e.g. useless... Fortunately shade encroachment during the winter months will be negligible. A bit during summer mornings, but only because of a tree that I want to replace anyway... As to radiation angle, I want maximum collection about 45 days on either side of the winter solstice. Looks like 50 degrees is about right, but I'm not sure yet. Panels are Viessmann Vitosol 300.

I printed that manual long ago and have studied numerous times. Unfortunately, it (like most others) is based on averages with regards to insolation as well as strictly conventional applications. For instance, it assumes that combined space heating/DHW applications do not work... Very little help when I'm trying to estimate solar input on an hourly basis... Do you have the attached certification document? It's both helpful and confusing to me. Do you understand the "Efficiency Equation" and "Incident Angle Modifier" at the bottom? Doesn't look like equations to me. Are these perhaps values to use in "standard" equations? I have seen at least two "standard" equations for efficiency and don't seem to find one for incident angle modification. Can you or anyone possibly provide? Also seems odd that a collector specifically named as 2 square meters has 2 1/2 square meters of aperture area. In the way I'm attempting to compute, shouldn't I be using aperture area? That agricultural reporting station reports daily insolation in megajoules per square meter per day--just like the left side of the chart. The "Clear" value of 23 MJ/sq.meter/day only seems to happen around the summer soltice. That's what makes me think that the insolation values are based on energy received on flat ground and that I must compensate for the collector angle where the collector is effectively working with the energy received by its shadow... Again, such seems to work fine if the sun is higher--but not when it's lower. Around the winter solstice I get insanely high collection values like 150,000 btu/day for 2 x 2 meter (rated) panels at 45 degree inclination and the sun at 29 degrees.

Here's the certification certificate I mentioned. Sorry for the error.

why hourly basis?

i understand what you are up to, but aren't averages good enough? have you been here? http://www.thermotechs.com/usdata.htm gives solar out put for their collectors 10,20 and 30 tube. I understand they're the same collectors as veissmans. i see solar space heating working on the extreme shoulder season and could work all year if you could afford all those tubes!

Am interested in hourly information because in space heating mode the system will be working on the fly. Space heating mode is "all or nothing". It either meets the full system requirements or is allowed to heat until it's either used for space heating (until exhausted) or for DHW. BUT, space heating mode can ONLY begin when the actual heat loss of the structure is less than the minimum modulation rate of the boiler--e.g. the burner has to cycle "off" before space heating can begin. Using my three years of boiler datalogs, I'm identifying "candidate" days. These are days when the boiler is cycling during the hours from say 9 a.m. - 4 p.m. In general the outside temp will average at least 38F during these periods. In a typical winter these make up about 60% of the days when heating is required. Of course solar intensity varies in these days--from completely overcast to completely sunny. My sizing goal for the panels is to provide 5-7 hours of space heating--depending on time of year--to at least 50% of these days in a typical winter. When I compare operational datalogs of "candidate" days to the insolation data I notice that either the boiler has been cycling for most of the night (typically 1-2 hour "bursts") or it has been firing continually at or very near minimum modulation all night. In either case, the supply temp will hit it's maximum amount above target about an hour after solar insolation has picked up considerably--usually somewhere between 8:30 a.m. and 10:30 a.m. depending on how rapidly the outside temperature is increasing. Actual target temperature will be 85F or below (and falling as the outside temp is rising) but the system supply temperature will be about 12-15F higher--the "buffer" provided by my gravity piping is fully charged... Everything is in my favor. The "buffer" is fully charged. Target temperature is low and falling. Passive solar gain is increasing thus reducing the actual heat loss. The TRVs have reduced flow in the south-facing rooms to nearly nothing as merely the residual heat in the rads is sufficient to meet the loss. On really bright days the south-facing rooms will overshoot by 2-3F for a couple of hours--starting right around this time of day. Solar irradiation is rising rapidly. On a "typical" day like this, the boiler will not fire--not even "pulse" for 20-40 minutes. ("Pulses" are firings that last only a few seconds at maximum input at 2-10 minute intervals.) Then when it does fire it typically pulses for at least another half hour. Pulses are triggered when the boiler temp drops below 70F but the actual system supply temperature I can measure is quite 5-10F below target--VERY frequently 72F. If the outside temp rises above 45F or so, the boiler will pulse all day long. If it doesn't the pulses will be interrupted by one or two "bursts" when the boiler fires at minimum input for 1 - 2 hours. These "bursts" AGAIN charge the "buffer" in the gravity mains. My goal is to virtually eliminate the "pulsing"--even on moderately cloudy days. On sunny but cooler (say averaging 42F) days, I want to eliminate the "bursts" as well. I'll do this by blending in just water heated via solar to prevent the boiler from firing. Even if such cannot meet target temp, the boiler still won't fire until the system temp drops about 10F below target. With system temp below target the house will attempt to cool, but again passive solar gain will operate in my favor as it has reduced the true temperature required in the system. Only when the solar input is utterly inadequate will the boiler have to fire. See why I'm working with hourly insolation data? Not only do I have to identify "candidate days" (based on hourly daytime temp data and presumed heat loss), but I have to determine if the solar component has enough energy available to at least prevent the pulsing. I also have to estimate any "leftover" heat in the solar tank that while not sufficient in temp for DHW is sufficient to give the system a bit of a head start on some mornings... This will happen because the opposite sequence of events occurs in the afternoon. Passive solar drops off rapidly (increasing the heat load); outside temp falls nearly as quickly; target temperature increases and while the water temp in the solar tank may still be 80F or so, it won't be able to meet system demands. The solar tank will then sit all night but since it's well insulated and not very hot to begin with, loss will be minimal and it will still be adequate for the beginning of the next day should it prove to be a good candidate... I'd originally hoped that 1 3-meter panel would be sufficient, but since I have to mount it on an adjacent structure with lines running about 30' underground plus 10' down to the ground, I'll have significantly more transmission loss. 2 x 2-meter panels [look] like they're going to work, but am still having problems estimating the possible input.

Didn't mention: www.thermotechs.com was very useful. Gave me the ability to estimate collection efficiency on an hourly basis. THANK YOU! Of course the delta-t problem is interesting as well. To keep efficiency up I have to keep average temp in the header of the solar collector as low as possible. Water surrounding the lower coil (providing the solar input) of the dual coil tank should be around 75F. Have to study the heat transfer ability of that coil carefully--thank heaven Viessmann provides GOOD data!--to see how high I can keep the flow rate (thus lowering average temp) without imparing the ability of the coil to transfer its' heat to the tank on a real-time basis. In a perfect world, fluid will be entering the solar header at 75F or so, leaving at no more than 85F or so with all of the gain instantly transferred in the coil.

I forgot to attach the certification document and am not at the right computer. Will add as soon as I can.

insolation efficiency?

Looking up my info for your state - it would suggest that 4-5 kwh/sqM is an annual average for available insolation. Your orientation to due south, encroachment of shade due to buildings/trees and the efficacy of your collectors all factor in too. If you wish to track this as accurately as you did relative to the vitodens install - might need to develop your own criteria and measurement methods. And do you wish to fine tune for winter radiation angles or summer? BTW - which panels are you considering?

Presuming that those insolation values are as collected on flat earth... Here's my area specific theory: Sunny winter days around here tend to be clear--glaringly clear. Summer days however are rarely clear--there is a nearly perpetual haze of humidity. This sets up a situation somewhat contradictory to the conventional wisdom of "you have the least when you need it the most". The most available solar energy [seems] to be available when I need it the most. While the most may be available then, a BIG part of the solar efficiency equation kicks in--difference in temperature between the air around the collectors and the fluid running through them. While the most may be avilable, you're loosing the most due to temperature difference--since, after all, it's cold in winter.... That's where I'm trying to use the solar energy to its best use regardless of the time of year. DHW preheat--I notice VERY often now that "preheat" is used instead of full domestic hot water heating--is not going to be the most efficient use in my system! DHW load is typically low during mid-day with the only exception being laundry day. With no DHW going out, you're not "pre-heating" you're HEATING! When AT LEAST 25% of my heating days (say from mid-October - mid-march) can be satisfied with no more than 85F supply with a return at or near ambient indoor temp it sure seems to me that the best use of the solar is for space heating. The clincher is that I get decent passive solar gain such that my actual heat loss might be 40% of that expected via Manual-J on a sunny day when the mid-day temp exceeds 38F or so.

Vitosol

reacts nicely with UV - so bright sunlight is not required. Are you able to look at your daily UV index on an annual basis too? And yes there will be periods of time when your solar system is heating and not preheating dhw - which is why Viessmann Mfg Co Inc offers (developed?) the bivalent indirect. And there are several piping possibilities available to tie in the solar with your Vitodens - especially at your ultra cool supply temps. You might be surprised with the results. I have added just one solar system to an existing vitodens - but with LLH. You might have to phone either Waterloo or RI for their take on installation details without it.

I've talked with Viessmann numerous times. The piping and control method I'm going to try is to my (and Viessmann's) knowledge unique. I'll be using the Comfortrol in a way nobody ever intended to provide the bulk of the control. It won't know what it's actually doing, but it won't care as to it, everything will seem "normal". I'll also attempt to use the Vitosolic 200 in a completely non-standard way to provide nearly all of the rest of the control. Why make custom when it's possible to use what's available--even if you're not doing so in the way they were originally intended to be used? For reasons I can't divulge I'm not at liberty to elaborate on the piping and control. If everything works, it will be really sweet and amazingly simple. If it doesn't work as planned it will still provide solar DHW without any modification. It [should] be adaptable to some systems using the LLH, provided they have true constant circulation on the secondary side and can operate at quite low temperatures during the daytime hours. Some slight daily daytime setback (the Vitodens way--e.g. setback of space temp via setback of the heating curve) could prove quite beneficial--particularly if the system doesn't use TRVs or FHVs.

comfortrol -

yes - if one looks carefully at the architecture - there are a few available inputs/outputs. One just has to look sideways at it for a day or two ...

A.T.

Mike, Following offered as background for what you're after. Illustrative purposes only. Certainly doable for your site with the right information. Sounds like you want to compare seasonal, daily (or hourly) solar flux. We have an Eppley PSP pyranometer (very high end; often used to calibrate other pyranometers). It collects data at 10s intervals and outputs hourly averages. You can use data for measured solar flux in conjunction with the solar flux calculated with no atmosphere. Done properly, this calculation also accounts for time (hour, day, year) and latitude. Attached is a plot of solar flux for 2003 at a location at ~41.5 north latitude. Pink is calculated solar flux with no atmosphere. Blue is measured daily total solar flux so it includes the effects of clouds, water vapor, etc. Two points here: 1) there is never (very rarely, actually) a day when you get more than about 75% of the possible flux; and 2) time of year trumps clarity of sky. Those clear winter days just don't deliver the flux that a even a moderately cloudy summer day does. So for here, anyway, the conventional wisdom holds. Earth spinning the way it does, I doubt it's any different where you are. The top (nevermind the scale; I moved it up for clarity) shows atmospheric transmittance (AT), which is soradm/soradc and thus dimensionless with values 0-1. Basically just shows that there is not a huge amount of seasonality to this location's sunny and cloudy days (though in detail you can see the quasi-periodicity of fall and spring frontal passages). This would at least provide encouragement that even though seasonality dominates total flux, at least it's not an uphill climb against the clouds, too (i.e. still plenty of clear days in the winter -- it would be a different story if winters were also cloudier. Seattle, anyone?) And I remember that run of sunless days in early April. Something like 4" of rain that week, most of it in two days. For here's that's pretty good. Good luck. I think we're headed down similar paths for solar.

Thank you and EVERYONE! Little by little, I'm getting there...

Mike ..2 banks of 30 tubes at 50 deg will probably still cook your solar tank in the summer unless you dump the heat since it has to go somewhere. My tank will easily approuch the 200 deg mark. So in my case I need more tank/reserve even with seven people in this house using water. So i'm considering more tank and maybee moving the panels up to 60 deg tilt and leave them year round. Mike ..I'm real interested in your low temp heating results since my radiant stuff is not all connected yet and I nedd to dump this extra heat in spring and fall in my floor but its in the works!! Paul

Hi Mike. I'm at 44 deg latitude.( 30 miles north of rochester N.Y.) I've set my panels at 55 deg for optimum spring and fall Btu's and then it helps to self limit the summer output simce my collecting area is oversized. I'm also off 25 deg to the east of true south.. I used to track my Sun hours(pump run times) for about 5 years. 85% of the hrs. were from March 15 to sept 30 . And the remaining 15% were after that in the winter. In other words very small amounts of btu's in the winter were the normal. On other hand I get alot of cloud and overcast blocking the sun and irritating me but i'm starting to get used to it. More to follow... Paul

I have an idea.

Mike, look up Zomeworks in New Mexico. See if you can get through to Steve Baer. He has a knack for taking the most difficult solar challenges and creating seemingly simple solutions. He WILL know ;~) Yours, Larry

AH -

self protection prior to vilification by the masses! :-) I seem to remember a "rule of thumb" back in the cobwebs somewhere, angle of latitude plus 22 deg for max winter insolation - but that might be for us canucks. For MO - that would put it at 58 - 62 deg inclination. And look at this site - http://www.retscreen.net/ang/home.php - but I think this site is focused on estimated savings - but its still worthwhile poking around its corners. I too am putting in the H30 panel and plan to chart its performance via a few extra temp sensors and the flow meter built into the Divicon. A known flow with a known Delta T will give you the number I think. DWH preheat is my primary goal - we'll see if there is any residual for a heating panel in the office (book keeper is always cold).

self protection prior to vilification by the masses! Not so much self-protection as awareness of what will happen... Is there any real wonder why objective comparisons between space heating methods are nearly as rare as hen's teeth?

I certainly have that manual and have studied it well. Still doesn't seem to help much however when it comes to attempting to use actual insolation data to estimate output on a short-term (say hourly) basis. Do you have the attached document? Can you make out the "Efficiency Equation" and "Incident Angle Modifier" notations at the bottom? They don't look like equations to me. Are they perhaps values for standardized equations for such computation? If so, I've seen at least two different "standard" efficiency equations and haven't yet found an "Incident Angle Modifier" equation. Can you or anyone provide?

I've searched and searched and can't seem to find the answer to these questions. 1) Insolation (both daily total and hourly average) are available from a nearby Agricultural Weater Reporting Station (Under "Weather Location" at the top, "Delta - Cape Girardeau County" is closest to me--about 10 miles away.) By the definition they provide, the values should be the energy received per square meter on flat ground. Is this correct? The data (hourly and as the sun changes inclination through the year) seems to verify this. e.g. the closer to solar noon, the more energy; and the closer the sun to directly overhead at solar noon the more energy on a similarly clear day. If correct then a collector of 1 square meter flat on the ground would have this much solar energy available, right? Again if correct, it's the actual angle of the solar collector that's causing me problems. See drawing named "Perfect Collection.jpg". Collector is at 45 degrees and sun is striking it perpendicularly. Am I correct that it is receiving the solar energy as striking the "this much solar" line? (Think only of solar noon.) Now see the drawing named "Sun Too High.jpg". This seems fairly straight-forward as well. As the sun becomes higher and higher, the "this much solar" line gets shorter and shorter. This would [appear] to self-compensate for the less-than-ideal sun-to-collector angle. Now see "Sun Too Low.jpg". Using the same logic as in the above, the "this much solar" line gets really long and it does not seem to self-compensate for the less-than-ideal angle. If I use these methods to compute the actual amount of ground "seen" by a collector of a given aperature area, it seems to work fine as long as the sun angle is not lower than the collector angle. As the winter solstice nears, I get what appears to be a ridiculous amount of available energy. How do I compensate?

flat on the ground

thats what i would think. when sun is overhead, summer, you get the highest energy per sq meter, anything less,spring,fall,winter, is less energy per square meter. Test: use a flash light, it puts out constant light intensity. when you shine on a piece of paper perpendicular you get the brightest light from the light beam. as you tilt the paper at different angles, you still have the same brightness from the flash light but now your light spot on the paper is larger, with same flash light output the energy per square meter has to be less. added: your drawings look somewhat correct, as in "sun too low". you should find that the large area in red will have the same power as the solar collector perpendiclar to the suns rays. one more added point here: both areas will have the same watts, not watts per sq meter!

Understand "test" perfectly. That's exactly what I'm asking. Are these insolation values based on the energy received in a square meter of flat ground or a square meter of energy if it were angled towards the sun? Regarding "added", that's sort of what I was thinking. Should I calculate the "red area" as if the collector were perpendicular to the sun and then apply the incident angle modifier? While I'm unsure of the source I did find a rather impressive solar design website suggesting that evacuated tubes still maintain about 98% of their possible output when 20 degrees off of vertical perfection. Do though explain your last sentence, "Both areas will have the same watts, not watts per sq meter!"

i could be wrong

but i think if you constantly correct for angle(s) you will get the same amount of energy year round minus the fact the days are shorter in winter. same energy per time then. so you'll still get x watts/sq m all the time, so to speak. ""Regarding "added", that's sort ..."" not sure what the incident angle modifier is? on thermomax's web site, incident angle correction is for panels not in optimum position when you need X output. yes, i would say the red area is the flat ground w/sq m surface, so project up onto the panel to get its output, shouldn't need an incident correction if i'm understanding correctly. last snetence: lets say you recieve 100 w/sq m on your 1 sq meter panel. so you are getting 100 watts, that red area therefore is also getting 100 watts but maybe its 2.2 sq meters. thats what i was driving at.

Install sheet for a quality thermopile pyranometer

http://www.kippzonen.com/download/kipp_instrsheet_cmp22_1721.pdf

Had a reply from MO Dept of Agriculture. This is the sensor they use throughout the state. Sure looks to me like it measures insolation as received on flat earth.

original post

what values of sun intensity did you use for the 3 sketches you posted? the 3 pictures seems correct, just unsure of the math you used? what does 'self compensating' mean?

Go back to wikipedia

I've scanned mainy topics there, if you read closely you should find all your answers. as others have said use trig to figure projections, or carefullly draw diagrams. your first paragraph, as i said with the flashlight and paper. power= I cosine theta : I=sun intensity approx 1000watts theta = your latitude + earth tilt, 23 degrees mid winter. 2nd par. look at flashlight experiment again. also answer found from one of my posts, info i found in wikipedia 3rd par. real time & storage basically the same thing. say you have 'good' sun from 9am-3pm. thats 6 hours. break that up into 180 deg. you get peak output only during 1 hour or at noon. (example only, it could be at 1.30pm) so now you have an equation relative to time of day, Power=I*sin theta, 0-180 degrees. thats a close estimate of hourly data, you could easily derive this from the monthly charts thermomax has. last par. I don;t understand. you should be clocking your gas meter, from 9am - 4pm, do that for a week or two. look at the thermomax charts to see how many tubes you'd need. its all about btu need, system doesn't know if you are heating DHW or radiators! I DO agree, doing all those back calculations can be fun. 3rd par.

An Interesting Comparison

CC.Rob kindly graphed our data together. Same period, same unit of measure but I have no idea if the measuring equipment itself is the same. See attachment. Hope you don't mind that I shared Rob. Light blue line is here--dark blue line is his (about 200 miles north by latitude difference). He's in NJ, I'm in MO. Would seem to support my idea that average summertime insolation is relatively reduced here while wintertime peaks are relatively high.

23Mj/m^2/day

gotta fix my numbers here. i would check that number again. most sources i see suggest the equator gets 1,000 watts/m^2. at your lattiude that comes to about 760 watts/m^2, peak, summer. or 2,600 btu's. 1,000 watts * cos 40 deg.

can't count on sun

since it varies so much on weather, I think the only thing you can rely on is averages, daily or monthly averages. hourly might work today, but not for the rest of the week. let the solar do as much as it can do, then kick in the boiler.

Here's a chart for measured solar radiation here during the same year. Did my best to scale it so that the overall shape would be as similar as possible to your (3x as wide as tall for this part of the data area). I don't know yet what instrumentation is being used for this day, but have written asking the question. Peak winter seems to be a bit higher on average than yours (makes sense as you're about 200 miles north), but notice summer. The peaks are significantly lower. Could this be the result of our nearly perpetual haze of humidity in the summer months? Even on "clear" summer days around here the sky is rarely blue like it is in the winter. Instead it's usually an ugly grey. With a collector angle optimized for early November and late February it sure [looks] like I can get some pretty decent collection at those times while maintaining fairly even overall collector efficiency. While outside temp is certainly lower around the optimal time, the fluid temp in the collector's header when it's supplying space heating should be at its lowest for the year as a whole--rather like solar DHW production in central FL.

daylight

[EDIT. Math error. Back to thinking board.]

Here's a chart for measured solar radiation here during the same year. Did my best to scale it so that the overall shape would be as similar as possible to your (3x as wide as tall for this part of the data area). I don't know yet what instrumentation is being used for this day, but have written asking the question. Peak winter seems to be a bit higher on average than yours (makes sense as you're about 200 miles north), but notice summer. The peaks are significantly lower. Could this be the result of our nearly perpetual haze of humidity in the summer months? Even on "clear" summer days around here the sky is rarely blue like it is in the winter. Instead it's usually an ugly grey. With a collector angle optimized for early November and late February it sure [looks] like I can get some pretty decent collection at those times while maintaining fairly even overall collector efficiency. While outside temp is certainly lower around the optimal time, the fluid temp in the collector's header when it's supplying space heating should be at its lowest for the year as a whole--rather like solar DHW production in central FL.

re insolation data

ISTR that the book 'from the ground up' had all the data needed, but I havent looked at it in a while

As to the answer to your origional question I'm pretty sure its calculated at perpendiccular to the sun. since that is Max BTU's at full sun/exposure. Correct me if I'm wrong.!!!

Completely agree that you "can't count on the sun" other than it will rise tomorrow... Six years of insolation and temperature data should give me a reasonable "average" when it comes to: 1) Determining days that are candidates (by average daytime temperature) for solar heating and; 2) Determining how many of those days (on average) can be supplied via solar. These are the reasons I'm looking at least daily (if not hourly) averages. Will though say that the numbers are confusing to say the least. Most amazing to me is that I find NOTHING regarding my original question. With solar energy measured FLAT ON THE GROUND how do I translate that to a tilted collector? Surely it's somehow related to the shadow of the collector... 49%-51% of the sizing is going to wind up based on my personal observations and experience and I won't even touch on the 2.5 sq. meter aperture area of the 2 meter rated panel... The fortunate thing is that no matter how I play with the numbers I wind up with a system that will nearly eliminate daytime "pulsing" of the boiler with 4 square meters (rated) of panel.

wikipedia?

i assume you've been here? http://en.wikipedia.org/wiki/Insolation The insolation into a surface is largest when the surface directly faces the Sun. As the angle increases between the direction normal to the surface and the direction of the rays of Sunlight, the insolation is reduced in proportion to the cosine of the angle. This is known in optics as Lambert's cosine law. This 'projection effect' is the main reason why the polar regions are much colder than equatorial regions on Earth. On an annual average the poles receive less insolation than does the equator, because at the poles, the Earth's surface is angled away from the Sun. from: http://en.wikipedia.org/wiki/Sunlight The World Meteorological Organization defines sunshine as direct irradiance from the Sun measured on the ground of at least 120 W·m−2. lots to read on this site!

Been there as well as many other places. Say you're on the equator with the sun directly overhead. You get X amount of solar energy per square meter of ground. Now move say 40 degees of latitude north. Neglecting the "transmission loss" for the added atmosphere through which the light must pass, isn't there the same amount of energy available to one square meter oriented at a 90 degree angle to the sun? BUT, if you're measuring on flat earth the amount of energy in that square meter on the equator has been "spread out" into a significantly larger area. Isn't this why we tilt solar panels and sometimes even "track" the sun? Unless a HUGE amount of energy is lost via "transmission loss" through the atmosphere, the insolation data to which I provided the link gives all appearance to me as having been measured flat on the ground. How can one square meter at an angle receive the same amount of energy as one square meter flat on the ground? This seems to me to be an incredibly basic question and it amazes me that I can't find much in the way of an answer--let alone freely available equations for estimation. Perhaps it's out there in "F-chart" based programs, but from what I've read such cannot be used for real-time solar collection as it's based on the assumption of storage. Perhaps everything just "averages out" during a given year--provided the collector angle stays fixed and the job (e.g. average fluid temp in the collector) stays about the same. Change that job however (say between a relatively high temp--DHW production--and a relatively low temp proportional space heating at or near its lowest required temps and I'd suspect that things no longer "average out".

goto bottom post

sorry, i put my suggestions at the bottom of the thread. read "go back to wikipedia"

Maybe it's too simple...

If you now believe they level the measuring devices, why not use simple trig? You know the angles.

I agree

I agree, max performance.

collector performance

The ability of a solar collector to capture radiation varies a small amount with the angle the sun strikes it. Called the "incident angle modifier". Measured from 0 to 90* vert. & horiz. across the face. the values are reported as a % of expected performance. For flat plate, always reps a decrease. For ETC, often can be a small increase. Best performance is measured @ right angle to the sun.

something totally different!

my design I'm working on is totally different. first problem is the boiler will be oversized, smallest munchkin still too big. so I need a buffer. the solar collectors will act as a priority boiler, whatever 'heat' is needed will come from the buffer/solar tank. the outlet of the buffer will have a motorized mixer so it can operate as if it were a modulating boiler. we can't "hope" for constant weather thoughout the day, so the collectors will heat the buffer tank as high as possible, the mixer will give the temps required by the radiant, as in outdoor reset. my idea is to use solar whenever possible, not just under modulation minimum levels. this includes DHW.

Only real difference I see here is that you might not have TRVs or similar to provide a real-time load to the boiler.

??????????????

what could be more real time than the structure itself? if panel rads are used, yes, i'll put trvs on them. floors will run on their own off buffer temp.

I'm not sure that all control systems give anywhere near the level of feedback from the structure itself as a constantly circulating, satisfied, TRVd system with proportional flow. The more I study, observe and live with proportional control (e.g. TRVs, pneumatics), the more I'm convinced that the best benefit is its ability to compensate for passive solar gains as they naturally move through the structure each day. Unless passive gain is so great that flow through a given radiator utterly stops, the system gives all appearance of "moving" passive solar gain into other radiators. I'm not saying this actually happens--just that it appears to happen. As recently as a couple years ago, I considered this implausible if not impossible--I learned a LOT from the season-long "Eurocave" experiment... As long as they're not too massive (say tube-in-concrete) floors controlled via FHVs [should] be able to do similar. Warmboard would seem to be an ideal candidate as it combines relatively low mass with a relatively large and highly conductive emitter.

how much tank do you have? Im' putting my tubes on the wall this month @ 65* in Maryland.

Paul B & Dr. Al 80 gallons for the solar tank itself and 120 gallons for the indirect DHW tank. 24-7-365 DHW recirculation (currently gravity but will probably have to switch to forced with the Viessmann indirect as it has a down-turning outlet) with a large Myson towel warmer as the highest, farthest element of the DHW recirculation system. While the DHW recirculation loop is nicely insulated and the towel warmer doesn't appear to be too much of an energy consumer when fully loaded with towels, there's certainly a constant, low-level load. Personally, I'd prefer that the dual-coil solar tank were about 40 gallons, but I doubt that Viessmann could fit their very generous HX coils in a tank that size... The Viessmann evacuated tube collectors are designed to be self-limiting and while 200 gallons of storage isn't huge, it's certainly within generally regarded as sufficient specs for the amount of collection I'm considering. Seems to be very little chance of "cooking" the system.

> Didn't mention: www.thermotechs.com was very
> useful. Gave me the ability to estimate
> collection efficiency on an hourly basis. THANK
> YOU!
>
> Of course the delta-t problem is
> interesting as well. To keep efficiency up I
> have to keep average temp in the header of the
> solar collector as low as possible.
>
> Water
> surrounding the lower coil (providing the solar
> input) of the dual coil tank should be around
> 75F. Have to study the heat transfer ability of
> that coil carefully--thank heaven Viessmann
> provides GOOD data!--to see how high I can keep
> the flow rate (thus lowering average temp)
> _I_without_/I_ imparing the ability of the coil
> to transfer its' heat to the tank on a real-time
> basis.
>
> In a perfect world, fluid will be
> entering the solar header at 75F or so, leaving
> at no more than 85F or so with all of the gain
> instantly transferred in the coil.

I started my trip 2 years ago and found that most couldn't give the actual estimated BTU due to solar variability. . As a former scientist, I liked the numbers to add up. I would have thought there would be a base line most referred to. SO as it seemd I could guess just as good, this is what I've come up with. I have built a well insulated not super insulated 1000 sqft addition with triple pane double argon windows that are directional for solar gain in the winter months. (I have almost 40% glass, most due south) Additionally, A heatpump as a terciary back up when I did not have enough storage heat and the temp outside was preferentioal. (this way my collectors can work when conditions are less than ideal) I have also gone with a manifold of 100 solar tubes @ 75 degress to accent the winter advantage and decrease the summer here in Maryland (38*). THis is to supply DHW and hot water for radiant heat in the winter and futer ice melt for the side walk (and sumer heat sink) Two double coil solar tanks with a in line electric tankless boiler for water back up. No SUPRISE... I am heating a concrete slab and warm board. Both estimated to run @ 110 and 87 degrees respectivly will creat damand for reseve supply. (due to the issue listed below I am planning to make both run @ 100 degrees) this is where I come to full stop. I'm looking for heating management system to control all three heating systems. It would need to be active first on time, then on outside temp, then solar collectior temp, then on tank temps, then inside temp, ect. Any ideas?

Wasn't using any particular value of intensity for those sketches--just the area of flat ground that's in the shadow of the collector itself. By "self-compensating" I mean that there's no attempt to adjust the collector angle side-to-side (as sun goes across the sky each day)--just to adjust the collector angle front-to-back to compensate for the elevation of the sun. Again, this assumes insolation as measured flat on the ground. Evacuated tube collectors seem to be quite tolerant with regards to horizontal incidence angle. By the time the sun is high enough that a decent amount of insolation (again assuming measured flat on the ground) is measured, the horizontal incidence angle modifier seems to be above 90% and growing quite rapidly. If I'm doing this at all correctly, I should be getting fairly close to an estimate of the solar energy available to the collector. If this is a "candidate" day I then assume that I'll be using the solar for space heating and compute efficiency using 100F average collector temp. (Believe though that it can be done with an average temp as low as 90F). If not a "candidate" day I assume the solar is being used for DHW with an average collector temp of 140F. Am using the equation 0.82 - 2.19 (Tm-Ta)/G to calculate efficiency where Tm is average collector temp, Ta is ambient temp and G is daily irradiance. (Guess I should adjust the equation for hourly instead of daily irradiance however.) Reasonably sunny "candidate days" seem to give about 80% efficiency. Sunny winter "non-candidate" days (too cold) have the lowest efficiency--around 75%. VERY sunny summer days have the highest efficiency--around 84% but more typically around 80% as well.

Have tried with the meter, but it's really tough because during the daylight hours of "candidate days" I'm generally using less than 1 therm and have to guess as 10ths of therms. Appears to be somewhere between 1/10th and 1.5 therms but I'm not utterly positive. I may be going at this wrong by attempting to find these "candidate" days where daytime temperature averages between 38 and 55F. If cloudy with nearly steady temps near the low end of that scale, real-time load and gas consumption are the highest with consumption at about 60% of that predicted by HVAC-Calc. If the day is quite sunny however passive solar gain [seems] to reduce the real-time load and consumption to about 1/3 of that predicted by HVAC-Calc. The passive solar gain seemed very high to me until I began to really pay attention to the sun and the surroundings. The front south-facing facade (not counting the 10/12 pitch hip roof) is 40' wide by 21' high. The street in front of me is a true boulevard--a divided street. All blacktop. The cross street dead ends (actually passes through to the far side of the divided street) at this boulevard right in front of my house--it's also blacktop. The boulevard and cross street have an upwards slope away from the house--probably about 5 degrees but increasing somewhat the further away you go. Considering the general angle of the winter sun, I seem to be getting a big reflection of energy from those blacktop streets onto the front facade of the house. Since I've "tuned" my body to be able to detect IR radiation from relatively low temperature sources I'd nearly swear that I can feel the radiation from the street--even on quite cool days.

theres your answer!

""""Have tried with the meter, but it's really tough because during the daylight hours of "candidate days" I'm generally using less than 1 therm and have to guess as 10ths of therms. Appears to be somewhere between 1/10th and 1.5 therms but I'm not utterly positive.""" how about clocking day and night and subtract the night, should give bigger numbers to read. so you are saying daily usage from 10,000 - 150,000 btu's? thats a huge spread. from thermomax web site, that requires 10 - 70 tubes, in summer.

Guess I could try that but will still have to estimate 10ths of a therm instead of to the nearest full therm. Have the high end of that consumption estimate wrong. Was looking at times of constant boiler firing at minimum input through the day--average outside temp around freezing. This is NOT one of my "candidate days". Max on a "candidate day" is more like 3/4 therm or 75,000 btus but when consumption is that high, it's likely rather cloudy even if it is a "candidate" by average daytime temperature. Don't forget that my real goal here is to eliminate as much of the "pulsing" operation of the Vitodens as possible without greatly oversizing the collectors for summertime DHW. At least I won't have to feel like such an energy hog when the "car wash" shower (it can flow at least 12 gpm if you turn everything on) and 95-gallon minimum Jacuzzi tub are used.