Title ..

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Heating Performance

Thermal Camera Pictures

Temperature Environment



Configuration  -- January 4, 2013 Test

In this test, the sunspace has been optimized for space heating the attached house via the in the following ways:

This is a mean, lean, heat making machine!

In this test, black weed fabric is suspended vertically down from the

The idea is to see if having this vertical absorbing fabric will get the hot air up to the ceiling more efficiently.  The day two test drops this fabric midway through the test, to compare h

One of the two 10 inch Grainger fans
that push air out of the sunspace.
The duct is extended outside to provide
a long straight duct for more accurate
flow measurements.
The vertical weed fabric screen used
in one of the configurations is also visible.
Setup for this test.
North wall is to left, weed fabric hung from
ridge line to right.  The vertical pipe has
temperature sensors at 3 ft and 6 ft off floor
between fabric and north wall.
The blue tape spots mark places where surface
temps were taken.
Same configuration with vertical weed fabric
and picture taken on south side of the fabric.
The vertical PVC pipe has two temperature sensors.
The blue tape spots mark places where surface
temps were taken.
eat production with and without it.


Floor is some sand over dirt followed by
a layer of 1.5 inch thick Styrofoam
rigid insulation board.
Looking without the vertical weed fabric
in place.  The weed fabric hangs
from the plastic pipe running below the ridge.
The floor is dirt covered with 1.5 inch
Styrofoam insulation with some plywood
walking strips laid on it, and black weed
fabric on top.
The two PVC pipe posts support temperature
Sunspace on one of the test days.
The two "tunnels" extending east and west from
the lower south corner preheat the flow
of inlet air a bit. 

Inlets and Outlets

The inlets for the sunspace are located on the east and west walls down low and just behind the south glazing.  In an attempt to prewarm the air coming into the inlet vents, a solar preheat tunnel was added to each inlet (see picture) .   while the inlets were cut as 1 ft square holes in the wall, they have been reduced to about 3 inches tall by 12 inches wide to prevent excessive flow and velocity through the inlets -- especially during windy times.

The outlets are located in the east and west ends near the peak.  Each outlet has its own Grainger 10 inch fan and is located about 4.5 ft from the east (or west) wall.  A straight flex duct runs from the fan outlet to the wall and outside the wall, the duct is extended another 6 ft by a straight 10 inch diameter metal duct.  The long straight duct run from the fan is intended to give steady  and straight flow at the outlet where velocity is measured.




This was a gang busters clear day -- not a hint of a cloud all day.  Its also only a couple weeks after the Winter Solstice, so the days are short and the sun is low in the sky (about 23 degrees at noon).  The outside air temperature was in the 20'sF.  Wind was generally light.

sunspace heating performance


Blue solid line -- sun intensity (w/sm)

Red Lines -- Fan outlet temperatures for East and West fans (F)  -- this is the temperature of the heated air going to the house for space heating.

Green dash-dot -- Ambient temperature (F)

Purple dash line - Temperature at about the 5 ft level in the sunspace (F)

The sunspace was run with the fans on to produced heat for the house from about 9:30am to about 1:30 pm.  At this point the fans were turned off to let the sunspace stagnate.  At about 2:15 pm the fans were turned back on again.

Total flow rate for the outlet ducts was 670 cfm (based on 614 fpm at outlet ducts).


Heat Production

Looking at the long period when the fan outlet temperature is around 100F and ambient temperature is about 26F, the sunspace is producing 670 cfm with a 74 F temperature rise. 

Heat Output = (100F-26F)*(670 ft^3/min)*(0.061 lb/ft^3)*(60 min/hr)*(0.24 BTU/lb-F) = 43,550 BTU/hr    (210 BTU/sqft of glazing)

This is about what a typical 60K BTU gas furnace would produce.

The heat output for the day looks like this:

Time Tout (F) Tin Trise Velocity (fpm) Duct Area (sf) Flow Rate (cfm) Air Density (lb/cf) Heat Out (BTU/hr)
10:00 AM hour 61 19.8 41.2 600 1.09 654 0.061 23668
11:00 AM 76.4 22.3 54.1 600 1.09 654 0.061 31079
12:00 PM 90 26.6 63.4 600 1.09 654 0.061 36422
1:00 PM 99.5 27.4 72.1 600 1.09 654 0.061 41420
2:00 PM 99.5 28.3 71.2 600 1.09 654 0.061 40903
3:00 PM 87 24.8 62.2 600 1.09 654 0.061 35732
4:00 PM 64 25.1 38.9 600 1.09 654 0.061 22347
Total               231570

So, about 232K BTU heat output for the day -- about equivalent to 3.6 gallons of propane burned in a 70% efficient furnace.

So, even this modest size sunspace can produce a lot of useful heat on a sunny winter day -- even for the shortest days of the year.



The fans were turned off at about 1:30 pm just to see what the temperature would to to with the sunspace stagnated.  The inlet vents were blocked with some (somewhat leaky) fiberglass insulation  and the outlets were left open -- so, there was likely some thermosyphon flow through the sunspace.

The temperature in the outlet duct gets up 166 F just before the fans were turned back on at 2:15 pm -- it probably would have climbed a few more degrees.  A temperature sensor closer to the peak got up to ???.

So, not surprisingly, this thing gets pretty warm pretty fast with no airflow.   While these temperatures are not dangerously high, some form of venting would be a good idea when the space heating fans are not running.

The odd looking double slope to the cool down curve after the fans were turned back on is because I initially forgot to pull out the fiberglass plugs I put in the inlet vents.  They came out around 2:45 pm, and the cool down slope steepens reflecting more air circulation.



One difficulty with making efficiency estimates from the performance curve above is that the even though this is a very low mass sunspace, it apparently has enough thermal mass that its outlet temperatures and heat output lag a bit behind changes in sun intensity.  You can see this in the time period from about 12:30 pm to about 1:30 pm -- in this time period, the output temperature and heat output are nearly constant at just over 100F, but the sun intensity is dropping from about 1130 w/sm down 1040 w/sm.  I believe that if the sunspace had even lower thermal mass, it would react more quickly to solar changes. 

This effect also shows up if you calculate efficiencies for the morning vs afternoon.  In the morning, the sunspace outlet temperature is lagging behind the sun level increases and producing lower outlet temperatures than it would if the sun just stayed steady at one level.  In the afternoon the sunspace outlet temperature drops more slowly than the drop in sun level because the sunspace mass is losing heat and keeping the temperatures up.  So, in the morning the apparent efficiencies are around 45% while in the afternoon they are more like 71% -- these are not really valid efficiency numbers in that conditions are not steady, but they illustrate the lag effect.

To get the best idea of efficiency that I could, I looked


So, how does this compare with a good commercial collector under the same conditions?








Thermal Pictures




Glazing Temperatures

These pictures need to be clicked on to see the temperature labels.

IR picture sunspace glazing
Outside of glazing.
Emissivity 0.95.

Inside  of glazing -- top.
Top part of glazing panel.

Inside of glazing - bottom.
Lower part of glazing panel.

Glazing pictures at 1:46 pm.

The left picture above is of the outside of the glazing with temperatures ranging from 38F at the bottom to 52F at the top.

The center picture is of the inside of the glazing near the top (the space is confined enough that I can't get the whole panel in).  The temperature is 103F on the inside surface, so the temperature difference across the twinwall glazing is about 103F - 52F = 51F.  

The right picture is of the inside of the glazing near the bottom with a temperature of 68F.  Temperature difference inside outside is 68F - 38F = 30F.

At this time, the conditions are:

Ambient temperature 28F

Fan outlet temperature  99F

Air temperature inside near glazing at bar 1/3 of way up  86F

Sun 1125 w/sm

Solar input  73K BTU/hr

Heat output = 41.5K BTU/hr

Losses = 73K - 41.5K = 31.5K BTU/hr

If you use a glazing average temperature difference of 40F, and R2 for the glazing, then the rough heat loss through the glazing is (200 sf)(40F)/(R2) = 4000 BTU/hr, which is not remotely close to the 31K BTU/hr total losses -- I would have expected closer agreement?

Just as an Interesting Item

I took some IR pictures of two other nearby collectors that face the same way and are at the same tilt --

The left picture is the sunspace glazing at 3 pm with an outside temperature of 35 F in the center.

The picture to the right has two collectors.

The right is the solar shed water heating collector with twinwall glazing.  Its outside temperature is similar to the sunspace collector (4F warmer).

The collector to the right is an unglazed pool heating collector being used as the prototype for the Off The Shelf DIY water heating system.  Its outside temperature  is 92F. 

All three collectors were operating at the time.

Inside the Sunspace

Back of sunspace (north of the vertical fabric curtain):

You have to click on these pictures to see the temperature labels

North roof behind fabric curtain.
Curtain is visible to right.
East fan is the circular item.

North wall and north ceiling.
Lower part of north ceiling and all
of North wall are shaded by the fabric curtain.

Lower part of North wall.
Fabric curtain out of view to the right.

All done with temperature range of 60F to 160F and emissivity of 0.95.

Front of sunspace (south of the vertical fabric curtain):