Maker Pro
Maker Pro

An Allentown house

NREL says 800 Btu/ft^2 of sun (300 diffuse) falls on a south wall on
an average 31.8 F December day with a 24.4 and 39.2 daily max and min
in Allentown, near the PA Renewable Energy Festival, 9/22-23/07,
http://www.paenergyfest.com, where I'll be talking about the system
below at 2:30 on Saturday and Nathan Hurst will talk about his Mazda
radiator solar heating experiments in Australia at 3:30 on Sunday.

Rich Komp (author of Practical Photovoltaics) will discuss energy-efficient
food storage at 3:30 on Saturday and new PV developments at 4:30 on Sunday.
We will all be exhibiting ourselves and a $35 1995 Mitsubishi 2.0 Eclipse
radiator at an "Ask the Engineer" table near Booth 24 in the exhibit area.

If a house is 65 F on average indoors (eg 70 F for 12 hours per day and
60 for the other 12) and a frugal 300 kWh/mo of indoor electrical use
provides 34K Btu of heat on an average day and a 4'x8'x3'-tall EPDM-lined
plywood heat storage tank on the ground containing 4x8x3x62.33 = 5984 pounds
of 140 F water warms the house using an 800 Btu/h-F radiator for 5 cloudy
days until it cools to Tmin and the house thermal conductance is G Btu/h-F
and we keep it 70 F on a 24.4 F morning, (Tmin-70)800 = (70-24.4)G makes
Tmin = 70+0.057G.

On an average day, we need 24(65-31.8)G-34K = 796.8G-34K Btu of heat energy.
If (140-Tmin)5984 = (140-(70+0.057G))5984 Btu = 5d(796.8-34K), G = 136 max,
and Tmin = 78 F, and the house needs 74.4K Btu/day of non-electrical heat.

A 1024 ft^2 house with a 640 ft^2 loft might look like this,
viewed in a fixed font:
 
Jeff said:
Nick, can you give us a summary of how this went?

Nicely :) Nathan ran the 2 fans in series on our Mitsubishi radiator
directly from a 20 W PV panel during his talk.
In particular I'd like to hear something of the Mazda Radiator experiments.

IIRC, he measured 972 W/C for the radiator, ie 1842 Btu/h-F.
That 800 Btu/h-F radiator has me thinking about low temperature supplemental
heating, just 10F over ambient yields a whopping 16,000 BTUs/Hr.

I was just estimating vs measuring 800 Btu/h-F. We could collect
800 Btu/h-F x 10 F = 8K Btu/h that way, no?
What I'm thinking of is storing the higher temperature water from the better
collectors and using lower temp collectors to add heat while the sun shines.
I suppose that would be like heat pump heat, not warm to the skin...

Sounds interesting...

One often-asked question was "What are you selling?" The answer was "nothing,"
which confused people :) Exit interviews said ours was the most popular of
the 102 booths.

Nick
 
Jeff said:
Is that with normal 12v running them? Or with the 20W panel feeding them
in series.

IIRC, he was using driving them with 60 watts total in a PWM circuit
vs 120 W full speed. Or maybe 16 watts... Each? This is a bit vague.
Seems to me the lower power, quieter version is far more desireable.

Sure. Over some range, power is proportional to cfm^3.
At any rate, I'm thinking of using 3 in a zone system (radiating,
not collecting) and would only need around 200 BTU/h-f out of each.

That means moving about 200 cfm, with perfect heat exchangers.
If a fan uses 80 watts at 1000 cfm, it might use 80(200/1000)^3
= 0.64 W at 200. Probably more. Maybe not much more.
Some time ago I had thought of using a hybrid of Bill Kreamers design
but with a small radiator in each to transfer the heat to water. Now I'm
thinking that collecting detached sunspace (or maybe big fin) heat and
pumping it into the house is a better idea.

"Large format," vs lots of boxes.
Gary did a long run with some of his collectors. I've got about a therm
of air collector (7' * 24')

One therm per day?
and will be adding about a therm of water (6 - 2' * 10' collectors
after Mike in NZ). I think another therm would put me in good shape.

Collecting warm air and hot water at the same time can be more efficient
than collecting them separately. Give the water priority in full sun,
and take as much air as possible at the same time.
... is there any reason for choosing the Mazda radiators?

I suppose that's what was in the local auto salvage yard.
Usually radiators are all pretty easy to remove and at my local junkyard
they are the same price.

I abandoned a dead '97 Ford Taurus after my mechanic said it would take me
3 days to remove its radiator. Remove the front bumper, then some large
structural metal pieces above and below the radiator, and so on. Toyotas
and other late model Japanese cars have 4 plastic posts... 2 drop into
holes below and 2 fit into plates above with 2 screws. Easy.
The secret to taking out radiators is a knife to cut the hoses.

Leave longish pieces attached to help connect them to standard plumbing
and pick cars with manual transmissions and no AC, other things being equal.
We (in the US) are a long way behind most of the world in thinking
solar. It's all those decades of being consumption orientated.

We don't export lots of valuable goods or services nowadays. Movies,
intellectual property, high-tech medical devices. It helps to reduce
waste and use what we have, eg dead cars and the sun. People say our
only growing resource is trash.

Nick
 
PA Renewable Energy Festival 9/22/07

100% Solar House and Water Heating with Sunspaces, by Nick Pine

It is commonly believed that houses can't be more than about 50% solar heated.
This is true of direct gain "mass and glass" passive solar houses, since
the windows lose lots of heat at night and on cloudy days and we have to live
inside the "heat battery," so the mass can't be hot on an average day, so
it can't store much heat.

If cloudy days are like coin flips, a house that can store heat for 1 day can
be at most 50% solar heated; 2 days make 75% possible, 3 make 88% possible;
4 allow 94%, and 5 allow 97%. More than 5 becomes uneconomical. Designing
for 100% solar heating begins with the local weather...

National Renewable Energy Laboratory (NREL) data say December is
the worst-case month for solar heating in Allentown, when 800 Btu/ft^2
of sun (300 diffuse) falls on a south wall on an average 31.8 F day
with a 24.4 and 39.2 daily max and min.

We can use basic high-school physics (eg "Ohm's law for heatflow," like
Ohm's law with different units) and algebra to determine how much insulation
the house needs, based on constant internal energy gains and a easily-built
heat storage tank: if the house is 65 F on average indoors (eg 70 F for
12 hours per day and 60 for the other 12) and a frugal 300 kWh/mo of indoor
electrical use (vs an 800 kWh/mo US national average) provides 34K Btu
of heat on an average day and a 4'x8'x3'-tall plywood heat storage tank
on the ground (with a single 10'x14' piece of EPDM rubber roofing material
folded up like a Chinese take-out box as a liner) containing 4x8x3x62.33
= 5984 pounds of 140 F water warms the house using an 800 Btu/h-F radiator
for 5 cloudy days until it cools to Tmin and the house thermal conductance
is G Btu/h-F and we keep it 70 F on a 24.4 F morning, (Tmin-70)800
= (70-24.4)G makes Tmin = 70+0.057G.

On an average day, we need 24(65-31.8)G-34K = 796.8G-34K Btu of heat energy.
If (140-Tmin)5984 = (140-(70+0.057G))5984 Btu = 5d(796.8-34K), G = 136 max,
and Tmin = 78 F, and the house needs 74.4K Btu/day of non-electrical heat.

A 1024 ft^2 house with a 640 ft^2 loft might look like this, viewed in a
fixed font:
 
Jeff said:
... If I solkoted (selective coating) galvanized roofing would I get
enough temperature rise as an unglazed trickle collector?

I suspect the coating wouldn't keep its effectiveness long outdoors.

Nick
 
Jeff said:
What's the verdict on trickle collectors, I haven't heard you talk
about them for a while?

It seems the big disadvantage is the need for glass as glazing.

That's one. I had thought polycarbonate might work before learning that
it won't last long in warm water vapor. Gary's looked into unglazed pool
trickle collectors at http://www.builditsolar.com. If we trickle down
water in a narrow channels that conduct heat in from nearby dry metal
surfaces, evaporation heat loss is less.

We might use an asphalt roof as a pool collector with a polyethylene cover
and something to hold it off the shingles to keep it from gluing itself to
the shingles when they are hot and dry in full sun, eg air inflation with
overhead straps to avoid wind fatigue.

Nick
 
The radiator and its fans could be at the top of a vertical duct that
returns sunspace air to the lower sunspace without mixing with room air.
On cloudy days, pump water up through the radiator to warm the house...

Air might flow as below, with no room air fan, just the 2 radiator fans
in series and an upper motorized sdamper, hinged at the bottom, with
a windshield wiper motor with limit switches that opens inwards up to 90
degrees (moving counterclockwise) to block room airflow in the horizontal
position, like this, viewed in a fixed font:

top 2' top
---------------------------- -----------
| r motor s. | | |
| a <--> d. | | |
| fd a. | | |
| <== ai <== m. 2' | | sdamper | 2'
| na p. | | |
| st e. | | |
| o 2' r. s | | (sdamper) |
| r-........-| u | |-----------|
| | ^ | n | s | ^ | cool
| | | | s | o | | | room
| | cool room| p | u 20' | --- | air east
| | air inlet| a | t | | inlet
| ----------| c | h |-----------|
| | e | | |
| | | | |
. .s | | |
. sunspace .d | | |
. air .a ^ | | |
.<== warm room ==> .m | | | sdamper |
. air outlet .p | | | |
. .e | | |
. .r | | |
---------------------------- -----------

cool room 12'
air inlet
| Drawing not to scale.
v
----------------------------
| r top s|s |
| fa view d|d |
| d a|a |
| <== ai <== m|m 4' | 12' south
| a p|p |
| nt e|e |
| o r|r |
----------r------------------
west
Modes:

1. To heat the tank, pull sunspace air through the radiator with its fans
and return it to the sunspace below, with the motorized sdamper horizontal
and Grainger's 4PC93 pump on if the tank is less than 140 F and the sunspace
is warmer than the tank. A lower one-way lightweight vertical plastic film
convection sdamper opens over a hardware cloth grate when the fan runs and
prevents reverse sunspace thermosyphoning at night.

2. To heat the house, pull room air through the radiator and back into
the room via the lower room air grate, with the upper sdamper horizontal
and the pump off if the sunspace is warmer than the room, and the upper
sdamper vertical and the pump on if the sunspace is colder.

3. To do both, alternate modes 1 and 2, moving the damper slowly, with
full action in about 5 minutes at a 1% PWM duty cycle. At full speed,
our '97 Ford Taurus wiper motor opened a 1' damper with a 3" pulley in
about 3 seconds. We put a 10 ohm resistor in series to reduce coasting.

house tank sunspace
<70? <140? >70? >tank? | damper fans pump notes
--------------------------------------------------------------------------
0 0 - - | up off off default
0 1 1 1 | down on on heat tank
1 0 0 - | up on on heat house with tank
1 0 1 - | down on off heat house with sunspace
1 1 1 1 | down on on heat house and tank

The room air temp might be 70 F during the day and 60 at night, with
a setback thermostat. The damper motor circuit might look like this,
with the damper normally down:

+12 --------------------------------------
| |
- opens when up, - opens when down,
| to limit travel | to limit travel
| |
| |
x close to raise - open to raise
| |
| lower |
| <------ |
| ----- |
|--------------|motor|-------------|
| ----- |
| |
| |
- open to raise x close to raise
| |
| |
| |
|--------------------------------------
--
The damper might look like this, in a fixed font: / \
/|motor&|
/ |pulley|
/ \ /
/ | -- |
-----------------------------------------------------------------
| . / |
| . / o|
| . / \
| . / |-
| r . / |s| upper limit
| . / f| | roller leaf
F | . / e|s| switch
| a . / l|-
| . / t|
| . / |
| d . / (up) |
| . <== / | <-- sunspace
A | . / | air
| i . / |
| . / | ~2'
| . / h |
| a . / i |
| . / n |
N | . / g |
| t . | (down) strape |
| . ---------------------------------------- |
| .| 1/2" plywood | |
| o .|----------------------------------------| |
| .| | |
S | .| 2" foil-polyiso board | |
| r .| | |
| .|----------------------------------------| |
| .| 1/2" plywood | |
| . ---------------------------------------- |
| . |
| . ~~~~~~~~~~~felt weatherstripping~o~~~~~~~~|
---------------------------------------\---------------------
^ |s s|
| ---- lower limit
room air roller leaf switch
Nick
 
The radiator and its fans could be at the top of a vertical duct that
We might have 2 motorized dampers, fully-open or fully-closed, like this:

----------------------------
.a motor r motor . |
.d <--> a <--> . |
.a fd . | heat water with sunspace
.m <== ai <== . 2' |
.p na . |
.e st . s |
.r o 2' . u |
|.......---r--sdamper-| n | s
| | ^ | s | o
| v | | p | u
| room | a | t
| air | c | t
| | e | h
. .s |
. sunspace .d |
. air .a ^ |
. ==> .m | |
. .p | |
. .e |
. .r |
----------------------------

----------------------------
. motor r motor s. |
. <--> a <--> d. |
. fd a. | heat house with water
. <== ai <== m. 2' |
. na p. |
. st e. s |
. o 2' r. u |
|adamper---r--.......-| n | s
| ^ | s | o
| | | p | u
| room | a | t
| air | c | t
| | e | h
. .s |
. .d |
. .a ^ |
.==> cool room .m | |
. air inlet .p | |
. .p | |
. .e |
. .r |
----------------------------

----------------------------
. motor r motor . |
. <--> a <--> . |
. fd . | heat house and/or water
. <== ai <== . 2' | with sunspace
. na . |
. st . s |
. o 2' . u |
|adamper---r--sdamper-| n | s
| ^ | s | o
| | | p | u
| room | a | t
| air | c | t
| | e | h
. .s |
. sunspace .d |
. air .a ^ |
.==> cool room ==> .m | |
. air inlet .p | |
. .e |
. .r |
----------------------------

with this simple logic:

house tank sunspace upper upper
<70? <140? >70? >140?| sdamp adamp fans pump notes
-------------------------------------------------------------------------
0 0 - - | up up off off default
0 1 - 1 | down up on on heat tank
1 0 0 - | up down on on heat house with tank
1 0 1 - | down down on off heat house with sunspace
1 1 1 1 | down down on on heat house and tank

Nick
 
We might have 2 motorized dampers, fully-open or fully-closed, like this:
----------------------------
.a motor r motor . |
.d <--> a <--> . |
.a fd . | heat water with sunspace
.m <== ai <== . 2' |
.p na . |
.e st . s |
.r o 2' . u |
|.......---r--sdamper-| n | s
| | ^ | s | o
| v | | p | u
| room | a | t
| air | c | t
| | e | h
. .s |
. sunspace .d |
. air .a ^ |
. ==> .m | |
. .p | |
. .e |
. .r |
----------------------------

with this simple logic:

house tank sunspace upper upper
<70? <140? >70? >140?| sdamp adamp fans pump notes
-------------------------------------------------------------------------
0 0 - - | up up off off default
0 1 - 1 | down up on on heat tank
1 0 0 - | up down on on heat house with tank
1 0 1 - | down down on off heat house with sunspace
1 1 1 1 | down down on on heat house and tank

We could lower the sdamper with an SPDT thermostat and 2 power darlingtons
when the sunspace is warmer than 80 F, like this, viewed in a fixed font:

sw* (open if ss<80 F)
+12 -------|----------------------------
| |
| sw 1K |
---X------------www---| |
| |
limit - open when - open when
switches | fully up | fully down
| |
| down |
| ----> |
|------sdamper------|
| |
| |----------------www---|
| | |
/ 1K / c |
-----www--| sw --www--|p TIP120 |
| \ \ e |
| | | |
| - - |
| |
---------------------------------------------

And lower the adamper whenever the house needs heat, with a setback thermostat
(the setback stores overnight heat in the house thermal mass):


+12 ------------------------------------
| |
/ 1K / e
hw* --www--| hw --www--|n TIP125
\ \ c
| |
| |
- open when - open when
| fully up | fully down
| |
| down |
| ----> |
|------adamper------|
| |
| hw | hw*
|------www---| |----------------www---|
| | |
/ 1K / c |
-----www--| +12 ---X--www--|p TIP120 |
| \ close \ e |
| | for heat | |
| - - |
| |
---------------------------------------------

And run the 2 12V fans when the house needs heat or (the tank needs heat
and the radiator is warmer than the tank) using a differential thermostat:

hw --------------------------------------->|--------- fans in series---|
open if |
tank > 140F |
------------- +12 --X--------|--------->|-------- f
|differential |-------uuu--- |
| | 120V relay | |--- tank
| thermostat |------------- w
------------- w
w
|
-

The pump would run with the fans, except when the sunspace is warm and
tank water is not being heated, with a NOR gate and a 12V relay:


f ---www------------ 120V
| |
/ u |
hw* ---www-----|p u X
| \ e u |
tank ---www-- | | --- pump
- -

As an alternative, we could control the system with a $99 Eway PC and
a single motorized damper and 5 one-wire DS18B20 temperature probes,
which would allow automatic passive room heating with less damper
motion and lower-power pumping after the pipes are full.

Nick
 
If outdoor air varies from 60 to 80 F on an average July day and the house
gains 34K Btu/day from 300 kWh of indoor electrical use plus 5K Btu of DHW
storage tank loss, with 6 hours per day of night ventilation, we need to
store 18h/24hx39K = 29K of coolth. If its thermal mass C warms from 65 F
in the morning to 75 by afternoon, (75-65)C = 29K makes C = 2.9K Btu/F.

A house with an inherent thermal mass of say, 2K Btu/F (1 Btu/F per board
foot of drywall, etc.), might include some basement mass for cooling, eg
900/55 = 16 4"x10' horizontal thinwall endcapped PVC water pipes tucked up
between first floor joists with a 3/4" hole on top and a #3 rubber stopper.
With more pipes or some uninsulated basement walls, we could store coolth
for a few warm days in a row.

In summertime, we could close the lower adamper and let outdoor air enter
the basement via a one-way window convection damper and exit via a summer
sunspace vent, like this, viewed in a fixed font:

------------------------------------------
| . motor r motor . .
| . <--> a <--> . . ==> (raise the upper damper to
| . fd . . stop natural airflow when
| . ==> ai ==> . 2' | the house temp drops
| . na . | to 65 F)
| . st . s |
| . o 2' . u |
| |--adamper-r--sdamper-| n | s
| | | s | o
| | | p | 20' u thermosyphoning night air
| | 2K Btu/F | a | t cools house and basement
| | house | c | t
| | mass | e | h
| a .s |
| d .d |
| a .a |
| m .m |
| ^ p .p .
| | e .e .
| | r .r .
|...........-------------.......---------------------
| 900 Btu/F | |
| basement . basement | |
| window mass | |
| damper . | |
| | |
| . . . . |
| |
| |
--------------------------------

During the day, we could run the radiator fans to cool the house with
basement air using a room temp thermostat and an occupancy sensor:

------------------------------------------
| . motor r motor s .
| . <--> a <--> d . ==>
| . fd a .
| . <== ai <== m 2' |
| . na p |
| . st e s |
| . o 2' r u |
| |--adamper-r--.......-| n | s
| | | s | o
| | | p | 20' u basement air cools house
| | 2K Btu/F | a | t during the day
| | house | c | t
| | mass | e | h
| a .s |
| d .d |
| a .a ^ |
| m .m | |
| | p ^ .p | .
| | e | .e . <== outdoor air cools sunspace
| v r | .r .
|...........-------------.......---------------------
| 900 Btu/F | |
| basement . basement | |
| window mass | |
| damper . | |
| | |
| . . . . | |
| ==> |
| |
--------------------------------

In 6 hours, 2 2'x3' vents with a 20' height difference and a 70-65 F avg
temp diff can move 6hx16.6x2'x3'sqrt(20')(70-65)^1.5 = 30K Btu/day.

Nick
 
Top