Bob Carruthers’ WOOD FIRED HYDRONIC
HEATING SYSTEM - LAST MODIFIED 3/15/04
(e-mail to (Bob Carruthers) )
ROBERT CARRUTHERS
ATMOS DC 40 GS WOOD BOILER
NOVEMBER 2003
Climate 100 miles north of Seattle (mild)
House 3,800 sq ft 12’
ceilings 11 skylights (1970)
Heat demand 400 therms plus in winter Months (cascade natural
gas bill $400)
Installation paired with existing Well-McLAIN GV6 175,000 Btu
condensing gas boiler
Existing Hydronic baseboard
(165*f plus operating temp)
Plumbing 1 ¼’ cooper primary
loop the three zones being secondary loops (1 ¼”)
Gas boiler has a pair of
Taco 007F circulator pumps built in. Wood boiler has one external Taco 007F
pump. Three zones each zone has a 009F pump.
Hot water storage 500 gal (converted propane tank ¼” thick wall) R19
6” fiberglass with tin cover
Large Extrol SX series
expansion tank (see pic)
Figure 1 Heating System
Figure 2 Self- activating
valve for cooling loop
Over heat protection for wood boiler
Self-actuating ½” valve
connected to cooling loop (Johnson V47AB4C) Normally closed. ($230)
Tripp-Lite automatic power
system 12-volt inverter charger 500 watts (car battery) ($165)
Figure 3 Backup power system
The Atmos boiler is designed
to operate at 80-90*c by way of a power regulator that controls the draft door
and an induced draft fan. At temperature the 007 circulating pump works
continuously.
System control
The system shown has an
auquastat (dp st) at the output of the wood boiler. When operating temp is
reached it locks out calls for heat to the gas boiler by opening the circuit
between house thermostats and gas boiler. It also makes a circuit to power a
relay that controls a three-way diverter valve that routes water around the
storage tank when tank temp is low (start up) giving the house priority. When
house does not call for heat the wood boiler heats the storage tank water by
way of the valve. In addition there is an aquastat (sp st) on the outlet of the
tank that locks out the diverter valve relay when the tank water is hot. The
water is then routed through the tank. These aquastats are adjustable and allow
fine-tuning. This system uses the Termovar (mixing valve) set @162*f for return
water boiler protection ($220) also used back flow check valves to prevent gas
boiler from heating storage tank water.
The system works well and
switches between boilers automatic
Figure 4 Expansion tank
Figure 5 Plumbing detail
Figure 6 Three-way diverter
valve
Figure 7 Relay and valve
Observations
When the pipe was insulated it
lowered the temp in the garage 15*f it also raised the temp of water in the
tank 10*. (195*f)
Uses average 18 cu ft of
wood per day
Opinions
Atmos boiler is the best
value I have seen it works well with dry wood and the gasification process is
easily achieved.
It will burn 3-4 hours under
heavy demand more than 6 hours average and more would be the exception.
When heat demand is not high
the gas boiler is more practical.
Heat storage
Radiant heat works better
than baseboard system as radiant demands a much lower temp than the 165*f
required for baseboard. For example I can hold 500gal at 195*f so that gives me
500gal at 30*useable before it reaches 165*f.
Radiant heat would yield 500gal at 100* of useable heat, before it
reached 90*-95*f over three times as
much as baseboard.
I think that the 500 gal tank is beneficial for efficiency but the
value of a larger tank for added heat storage would not be practical.
The tanks can be purchased
use from scrap yards ($.13 lb) ($150) Tank is easy to insulate it is supported
by a 1” rubber matt salvaged from horse trailer. Down side is cost of expansion
tank ($350)
This has been a project I
have enjoyed and am pleased with results.
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