I've been finding curiousities in Ramlow's 2006 book "Solar Water Heating,
a comprehensive guide to solar water and space heating systems"...
Not much, with a long payback. Airlock vestibules don't save much
either, unless you live in a department store :-)
At $0 vs $/ft^2? You can do both, with a sunspace, but you can't
live in a water heater. And why do solar water heaters have to cost
$K vs $K?
I doubt the 50 people in our 2004 ASES solar heating workshop
in Portland OR would echo that mantra.
Rubbish. Plain old glass lasts a long time, and $/ft^2 polycarbonate
lasts 20 years. A double-glazed polycarb panel can be reversed to expose
the indoor face to the outdoors for another 20 years. I'm 62 now...
But Bob was only talking about cloudy days.
Some concentrators don't move at all.
The most serious mistake was making the outer container of the receiver
of plywood. We thought that the plywood would be sufficiently insulated
from the copper panel which was the receiver proper, that it would not
get too hot. The copper panel was separated from the plywood by 4" of
fiberglass insulation. Nevertheless, the plywood caught fire and the unit
was completely destroyed. We suppose this is a success, of sorts.
The copper panel which was plated with chrome black to provide a
selective surface originally had a copper tube fastened to the back
by a high melting point soft solder. When we first attempted to operate
the unit, the soft solder melted, and the tubing became detatched
from the panel. We attempted to repair this failure by silver soldering
copper bars to the copper tube and screwing the bars to the plated
copper sheet. This worked, after a fashion...
The glass window was originally tempered glass. This shattered due to
thermal shock. We replaced it with ordinary window glass. This cracked
due to thermal shock, but we were able to hold it in place well enough
to make some measurements... The measurements we were able to make before
the fire generally confirmed our thinking concerning the design...
from "A solar collector with no convection losses," (a downward-facing
receiver over a 4:1 concentrating parabolic mirror), by H. Hinterberger
and J. O'Meara of Fermilab, in "Sharing the Sun," A joint ASES/SESC
conference, August 15th-20th, 1976(?), Winnepeg, Volume 2, pp 138-145.
Chlorine is death to many plastics.
Page 33 is about air heaters.
They work fine up to 170 F.
No. Floating ball check valves are important parts in many solar water
That is an open loop indirect system.
They can both happen in one tank.
A pump might only move 1 gpm up through a collector, until the return
pipe fills, making a partial vacuum, with more flow and no current
burst. Grainger's $89 4PC84 178 W pump can only move 3 gpm up 20',
but it can move 21.5 gpm up 10', after it fills a return pipe, like
a $01 4PC82 230 W pump.
Water freezes at 32 F, period. A trickle of fresh ground water can
keep a pipe above 32 F.
I think he is, over and over.
A bubble won't change the pressure reading.
More, beginning with solar space heating systems:
96 "It is impractical to have a heat storage mass that can hold
enough heat to do the job..." But PE Norman Saunders has been designing
practical inexpensive solar houses like this since 1946. He estimates
that some clients will only need to "purchase heat" every 35 years.
"On sunny days that are not as cold we will have excess heat and
could overheat something..." But winter overheating is easy to fix, just
turn on a fan or open a window. Or use smarter controls that don't
overheat the house in the first place.
98 Drainback systems are not unsuitable in freezing climates.
100 Why does gravity eliminate the possibility of remote-mounting
a collector array? :-)
101 Solar heat is not "compatible with all existing heat delivery
systems," and diversion loads are avoidable.
103 STSS EPDM-lined tanks (which easily fit through doorways when
compressed in their crates) have lasted a lot longer than 15 years, and
steel tanks can last a long time with a non-toxic corrosion inhibitor,
eg a 0.5% solution of ACI-100 (mostly sodium silicate) from D.W. Davies.
104 Caps on heat exchanger frames to avoid wearing holes in EPDM liners
are good, but a $0 13-gallon 1"x300' HDPE plastic pipe coil heat exchanger
seems better, with a 140 F max tank temp... 2" of foamboard insulation
isn't much. What about homemade heat storage tanks?
105 Why 1' of heat exhange tubing (what size?) per 4 ft^2 of collector?
Why the weird bulkhead fitting arrangement.
106 Why do we need a high-head full-flow pump for drainback, vs a 2-speed
pump or 2 pumps in series with 1 turning off after the return pipe fills in
a slow drainback system? Why 4' of friction head? A separate drainback tank
with a heat exchanger below seems like a poor way to avoid a high-head pump.
107 Why not mingle solar and conventional HVAC fluids? No mention that
efficient solar heaters have lower fluid temps which won't work well with
high-temp radiators. Why compromise comfort with 2 thermostat setpoints
instead of using smarter controls with a single setpoint?
108 The min tank temp depends on the indoor and outdoor temps and wind
and indoor electrical usage and the amount of sun shining into windows,
vs the fixed 85 F mentioned.
109 Why blowers and ductwork, vs passive convectors and floor returns
near outside walls as in old-fashioned gravity furnaces and Harry Thomason's
houses? Why not turn on a blower with a line-voltage thermostat?
110 A summer/winter switch seems awkward. PE Norman Saunders says a well-
designed solar house is just as likely to need cooling as heating at any
instant in wintertime. He provides a cool source (20K pounds of rocks in
the basement) as well as a heat source (10K pounds of water containers in
the attic) in his 100% solar-heated houses.
111 Standalone seems good. Bigger wire? :-) Fin-tube baseboard and cast-
iron radiators won't work well with efficient low-temp solar water.
113 Rich Komp's Maine house has a high-mass solar-warmed air hypocaust,
a 4" concrete slab over 8x8x16" hollow blocks over a vapor barrier. A small
PV-powered fan pushes warm air down from the top of the room under the slab
when the sun shines. Ernie the ermine takes care of vermin. High-mass solar
systems are not necessarily heated with closed-loop antifreeze.
114 The book describes 2' of sand as if it were a seasonal heat store,
but with no insulation above, at say, 80 F when fully-charged (if we have
to live inside the heat store), a 1200 ft^2 house with 504K pounds of sand
with a specific heat of 0.191 Btu/F-lb (vs 1 for water) with C = 0.191x504K
= 96.3K Btu/F and a low thermal conductance U = 200 Btu/h-F would have
a time constant RC = C/G = 481 hours. At the average 16 F January temp
in Madison, WI, it would cool from 80 to 70 F in -481ln((70-16)/(80-16))
= 82 hours, about 3 days. Or less, if we include the sand resistance. One
105 cubic foot of sand can store 0.191x105 = 20 Btu/F, the same as 20/8.33
= 2.4, not 4.8 gallons of water, and water is about half, not twice as
dense as sand, which is why we don't see sand floating on water :-)
115 "The first thing to realize is that it may take an entire year to
get the sand bed dry and hot." No... it might take a week, and it could
store 100x0.4x62.33/20 = 75% more heat if wet, with 40% water by volume.
OTOH, we might store heat in a 26 million gallon "water tank"...
The Lyckebo [Sweden] system is a cavern of 100,000 m^3 capacity, cut out of
bedrock using standard mining methods, of cylindrical shape, with a central
column of rock left to support the overhead rock. The cavern is about 30 m
high and its top is about 30 m below ground level. It is water filled, and
inlet and outlet pipes can be moved up and down to inject and remove water
from controlled levels. The water is highly stratified with top to bottom
temperatures of about 80 to 30 C. Figure 8.7.2 shows temperature profiles
in the store at various dates in the second year of operation... No thermal
insulation is used, and there is a degree of coupling with surrounding rock
which adds some effective capacity to the system. Losses occur to a semi-
infinite solid and can be estimated by standard methods. Observed losses
from this system are higher than those calculated; this is attributed to
small but significant thermal circulation of water through the tunnel used
in cavern construction and back through fissures in the rock. It takes
several years of cycling through the annual weather variations for a storage
system of this size to reach a "steady periodic" operation. In the second
year of its operation, while it was still in a "warm-up" stage, 74% of the
energy added to the store was recovered.
from p 404 of section 8.7, "seasonal storage," of _Solar Engineering
of Thermal Processes_, by John A Duffie and William A Beckman, 2nd
edition, 1991, Wiley-Interscience ISBN 0-471-51056-4
116 Heating floor mass with house windows open doesn't sound efficient :-)
117 "This fresh air is a real bonus..." :-) More manual shunt valves, ick.
Why do all high-mass systems need antifreeze and diversion loads? :-)
Whatever happened to draindown systems?
118 Hot tubs are better diversion loads than pex buried in soil, but for
most people, 103 F is too cool and 105 is too hot. Air can heat water, as
Nathan Hurst stored lots of solar heat in water from sunspace air using
an inexpensive car radiator with its 20 watt fans, vs "a substantial blower."
Air collectors can be more efficient than water collectors, and they can be
set up as systems WITH storage, as in the NH CSI HQ building, 100% heated
"with 98% sun power and 2% blower power."
119 Why not store heat in an air system? Lots of people have done this
successfully, including PE Norman Saunders. Bob fails to mention glazed
transpired mesh air heaters again, and says wall-mounted systems can't
heat buildings in summertime :-)
120 We don't need no steenkeeng ductwork.
121 Cold air won't flow through a hole unless it is rectangular? :-)
Air handling energy can be small, with large flow passages and fans
or slow blowers, and some motorized dampers only use 2 watts when
moving. Draindown systems don't need freezing heat exchangers :-)
122 "A promising technology that I have hopes for is the use of air
rising in a a solar chimney to spin an electric generator."
Here's a naive efficiency estimate for these "helio-aero-gravity" towers,
huge chimneys with wind turbines at the top surrounded by acres and acres
of greenhouses in deserts to make a "solar wind" up the chimney...
We can start with an old empirical chimney formula,
cfm = 16.6 Av sqrt(HdT), where Av is the vent area at the top and bottom,
H is the height difference in feet, and
dT is the (F) temperature difference.
The airstream's heat power in Btu/h is roughly cfmdT = 16.6H^0.5dT^1.5
for a 1 ft^2 chimney. With a constant power heat source (the acres and
acres of greenhouses), this equation naively implies that the taller
the chimney, the smaller the temperature difference and the larger the
air velocity. Smaller temperature differences are better, representing
less waste heat. We might think of chimneys as transformers that increase
the air velocity of a heat source and reduce the temperature difference.
For a 1 ft^2 chimney, the power density is 16.6H^0.5dT^1.5 Btu/h-ft^2,
and the air velocity V = 0.1886H^0.5dT^0.5 mph.
Paul Gipe's Wind Power book says wind power density is 0.05472V^3 W/m^2,
where V is in mph. He says the best rotors achieve 40% efficiency (vs the
60% Betz limit, which may not apply for a chimney)... 90% efficiencies
for the transmission, generator, and power conversion make the wind power
density 0.01596V^3 W/m^2 or 0.00506V^3 Btu/h-ft^2.
So the heat-to-electrical power conversion efficiency of the chimney
is E = 100x0.00506(0.1886H^0.5dT^1.5)^3/(16.6H^0.5dT^0.5) = 0.0002H %,
where H is the chimney height in feet. E = 0.002% for a 10' chimney,
0.02% for 100', 0.2% for 1000', and 2% for 10,000'.
This doesn't account for the heat loss through the greenhouse glazing or
chimney walls, or air friction in the chimney, nor the fact that the
weight and cost of a tower increase a lot faster than the height...
124 Why can't a system drain back to a tank in a basement?
125 "Here in Wisconsin... On June 21, the sun... is directly overhead
at noon (90 degrees from the horizontal...)" Bob says he lives at 45
degrees north latitude, where the sun would be 90-45+23.5 = 68.5 degrees
above the horizon at noon on 6/21. The sun would be directly overhead
on 6/21 at 23.5 lat on the Tropic of Cancer, in the part of Wisconsin
located in northern Cuba :-)
133 Why not get closer to 100% solar house heating? If cloudy days
are like coin flips, a house that can store enough heat for 1 day can
be at most 50% solar-heated; 2 days make 75% possible, 3 make 88%,
4 make 93%, and 5 make 97%. More than 5 becomes uneconomical.
135 Used utility kWh meters are cheap at about $0.
136 Storing 5 gallons vs 1 of hot water for every gallon of daily use
makes more sense to me. As an alternative, a large unpressurized space heat
storage tank that cools from 140 to 90 F over 5 cloudy December days might
preheat water in a pressurized plastic pipe coil 100% to 110 F for the first
3 days, 91% to 100 F on the 4th day, and 82% to 90 F on the 5th, supplying
a weighted average 98% water heating. A simple greywater heat exchanger
with storage could return most of the water heat to house air.
Then Bob talks more about "the risk of overheating," as if we can't just
turn off the pump in a simple draindown system :-)
137 A large well-insulated tank doesn't require a lot more collector
area for the same use. Why not store 10 vs 1-2 gallons/ft^2 of collector?
138 Overheating fears again. Turn off the pump! :-)
139 "In most climates it is nearly impossible to heat a dwelling 100%
with solar energy..." Given the random nature of weather, that's true in
every climate. PE Norman Saunders says he's never quite reached 100% in
New England, but having to "purchase heat" every 35 years isn't bad :-)
140 Sizing a solar energy system IS a precise science, given good
local weather data, including NREL's TMY2 and TMY3 hourly files.
141 "It is impractical to size a solar heating system to heat your
building on the coldest day of the year, because then for the rest of the
winter your system would be oversized." But that's how conventional HVAC
systems are sized, with a local "winter design temperature." Economics
may favor "purchasing heat" on very cold days, eg once every 35 years.
142 The gas bill analysis needs to include a furnace efficiency.
145 The big issue is NOT overheating! And the number of sunny days in
a month is less important than the average temperature and the average
amount of sun, eg 21.7 F and 810 Btu/ft^2 of sun on a south wall on
an average December day in Madison, WI. The average daily max is 29.8,
so the average daytime temp is about 26. Twinwall polycarbonate on
a low-mass sunspace would collect 0.8x810 = 648 Btu/ft^2 and lose about
6h(100-26)1ft^2/R2 = 222, for a net 426 Btu/ft^2 on an average day.
148 No mention of slow-draindown systems with less powerful pumps,
nor 2-speed pumps nor sequenced pumps in series. "Be aware that
centrifugal high-head pumps can only pump fluid to a height of 30'
above the pump..." shows serious confusion. They can only suck water
up from a 30' height above the water.
149 Why not "oversize" an air collector? :-) Bob suggests 10% of
the floor area as collectors. My 1536 ft^2 1820 stone farmhouse has
16'x32' of sunspace glazing and 20'x32' of Dynaglas attic glazing,
ie 75% of the floor area.
160 Another way to mount a "collector" (or studs on masonry walls)
is to glue it to a house with spray foam. I just bought 94 23 oz. Great
Stuff Pro canisters near the end of their shelf life for $.25 each
from Home Depot :-)
161 Collectors with clogged weep holes can explode? :-)
165 The book's S = 2Lsin((T-P)/2) equation produces a standoff length
of 12.53 inches with L = 48" and collector tilt T = 60 degrees and roof
pitch P = 45 degrees. Simple geometry makes S = Lsin(T-P) = 12.43". Fig
8.11 on page 166 says S = 13"(?)
167 "All collectors should be pitched slightly towards the supply end
to facilitate system draining"? :-)
171 Ice can be a good solar mirror, leaving collectors frozen in
full sun. We might melt it off by manually turning on the circulation
pump instead of scraping it off.
173 In most parts of the US, collector frames have to be strong
enough to withstand a 100 mph wind. Building codes specify max local
windspeeds and basic velocity pressure P = 0.00256V^2, eg P = 16 psf
at V = 80 mph. Gary Reysa and I are working on a simple very low cost
ground-mounted ICS "solar pond" heater with a pump.
178 Gary and I found that even small pumps destroy stratification.
190 Why commercial solar pool heaters, vs very simple systems, eg
trickling water between a roof and a large piece of 5-year 5 cent/ft^2
greenhouse polyethylene film? I'm helping a local YMCA with a 50'x75'
version of this.
204 Pump horsepower and head capability are not necessarily related.
A low-power gear pump might move a trickle of water up 300'.
209 ICS systems CAN have pumps.
215 A smart differential thermostat might circulate glycol to keep
it from overheating and continue circulation at night to cool the tank
to some upper limit. IIRC, some swimming pools work this way.
218 We need to OPEN- vs short circuit a negative tempco thermister
storage sensor to make the controller think it's cold. And ICS systems
can work fine in freezing climates. SRCC's OG300 spec includes a test
procedure for this.
222 Buy Tom Lane's book instead of this one :-)
228 Water vapor does not scatter light, and degree-days are not
230 Orientation includes tilt, and selective surfaces are poor
heat vs solar energy radiators.