COMMENT ⊗   VALID 00004 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002	\input LETT.tex \personal
C00004 00003	Solar Heating Calculations
C00014 00004	Data from the PG&E report
C00015 ENDMK
C⊗;
\input LETT.tex \personal
\date{June 22}
\to {Mr. Jack Dillon\cr 
The Sequoias\cr}
{\noindent Dear Jack:}

The Conservation Committee has reviewed the PG&E report dated September 4,
1981.

The PG&E report is quite voluminous. Unfortunately, in many cases it quite
fails to differentiate between the savings that would result from the
adoption of reasonable conservation measures, such as those that this
committee has been recommending for some time, and the savings that would
result from changes in our physical plant togather with the subsequent
adoption of essentially these same conservation measures.

We are inclosing two reports, the first one being an analysis of the PG&E
report as such, and the second containing the Conservation Committee's
recommendations for action.

\sign {\hfill Sincerely Yours,\cr\ssqip\cr \hfill Harry K. Farrar,
Chairman}


\fin % C'est tout.  \end
Solar Heating Calculations

Our total gas consumption for one year at The Sequoias amounted to 257,696
therms at a cost of $115,800. This is approximately 700 therms a day,
although, of course, our consumption varies from a low of perhaps 200
therms per day during the summer months for domestic water heating only to
as much as 1200 therms per day during very cold weather.

From the PG&E report it would seem that roughly one third of our gas
requirements are used in heating domestic hot water.  The PG&E report did
not made any recommendations regarding the use of solar heating to provide
a portion of our space heating requirements and only made some rather
feable recommendations as to the use of solar heating for domestic hot
water heating.  Unfortunately the PG%E analysis did not take account of
the interdependance of our existing equipment for space and domestic water
heating and of our need for a constant temperature domestic hot water
supply, which we now achieve by having a circulating systen and a heat
exchanger that has a capacity of roughly 400 gallons.

Our present installation uses the same boiler and the same distribution
system to provide the heat necessary for both space heating and domestic
water heating.  It seems highly unrealistic to separate the two needs when
considering a solar heating supplement, particularly in view of the fact
that at least two thirds of our gas heating requirements are devoted to
space heating.  So, in what follows, I will discuss the case where this
artificial isolation is not introduced.

It would seem reasonable to design a solar heating installation that would
halve our gas comsumption at a yearly saving of approximately
$60,000. This sets an upper limit on the amount that we should spend for
the system at perhaps $500,000, assuming that we would be able to borrow
at somewhat less than the going prime interest rate.

In the calculations to follow, I will assume that we will have $500,000 to
spend and that we will design the system on the basis of a net yearly
saving of 130,000 therms.

It would be to our advantage if we could design a modular system that
could be installed gradually over a period of time. This might suggest a
system in which each building were treated as an isolated installation
with its own solar panels and its own hot water reservoir. This would
require finding room for a relatively large reservoir at each building and
it would forgo the economies of size that would attend both the
construction of the reservoir system and its maintenance. Also it quite fails
to take advantage of rather spcial situation here at The Sequoias where we
already have in existance a hot water distribution system.  This existing
system can easily be modified to allow the solar heating units to be
handled on a modular basis at each building and at the same time to allow
for a central reservoir that would be used to store heat during those
periods when solar heat is produced in excess and from which all buildings
could draw heat during non-sunny hours.

Such a system would not require any modificationd to our existing
circulsting domestic hot water system, and it would not require the
location of additional water storage in each individual building.  It
would require the construction of a rather large centrally-located storage
reservoir.

Advantage would be taken of our existing heating system by having a
thermostatically-controlled water pump in each building that would draw
water from the normal return-water line and force it through the solar
panels and out into the hot water line during periods when the temperature
of the water from the panels was above the input water temperature and
also above some reasonable value.  During periods in which the solar
contribution was less than the local building heating requirements, this
would reduce the amount of hot water that the building would draw from the
central distribution system and during periods when there was an excess
amount of solar-generated heat there would be an actual reversal of water
flow in the distribution system.

As far as the overall system would be concerned the existing gas-fired
boiler would then be left with the job of making up any heat deficiency.
The boiler would be operated only during those periods when the heat
contribution from the solar panels was insufficient to meet the demand and
then only at the rate required to meet the demand without contribution to
any significant extent to the heat input to the storage reservoir.  This
would maintain a relatively large temperature difference between the water
at the very top of the reservoir and the rest of the reservoir so as to
make available as large as possible temperature range for the storage of
solar heat.


The heating of the water by the solar panels would not, of course, be subject
this same constrant and the water temperature in the entire reservoir would
be raised to the maximum possible extent during the solar heating periods,
always maintaining as large a temperature gradient as possible from the
bottom to the top of the reservoir to allow the maximum temperature difference
between the input water to the solar panels and the output temperature.

On the assumption that a temperature range of 100 degrees could be made
available for the water in substantially the entire reservoir and that
we would like to be able to store at least 300 therms, a reservoir capacity
37,500 gallons would be required. Since the reservoir need not be pressurized,
a convenient way of providing this capacity would be by means of a covered
circular underground  cement structure, of perhaps 25 feet in diameter and 10
feet deep. 

The exact ratio of depth to diameter would be a compromise betweem
the cost of construction, the availability of a suitable site for its
installation, the ease of maintaining an adequate temperature gradient from
top to bottom and the heat losses which would depend on how well the circular
side surface could be heat insulated and the losses through the top.
Data from the PG&E report
Totalelectrical comsumption for 1 year 2,218,500 kwh @ $127,000 
Total gas consumption 257,696 therms @ $115,800
They recommended savings of 408,000 kwh @ $23,255 and
24,606 therms @ $10,740

If we could save 1/2 of our total gas consumption the reduction in cost
would amount to $57,900, at,however, a substantial investment.