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The First Parish in Bedford Unitarian Universalist 75 The Great Road, Bedford, Massachusetts 01730 On the Common 781-275-7994 |
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The First Parish in Bedford Unitarian Universalist 75 The Great Road, Bedford, Massachusetts 01730 On the Common 781-275-7994 |
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The First Parish has two heating systems:
 | an oil fired hot air furnace that heats the Sanctuary &
Main Entrance and Coffee Room
 a gas fired Forced Hot Water system that heats the rest of
the building. This unit was installed during the great energy
crisis of the mid 70's. The new, efficient unit replace a oil
fired, single boiler unit. It's reported that the cost of conversion
was saved in the difference in oil and gas prices in the 70 &
80's
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The purpose of this document is to describe the operation of the Forced Hot Water system
| Zones layout
| Room temperature control
| Boiler temperature control
| Freeze prevention
| Problems & Cures
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The church is serviced by 9 zones, each zone has it's own pump. There are no thermostatically controlled diverter valves. The Zone numbers below refer to the order of the pumps from left to right as viewed from the back of the boiler.
| Basement
First Floor
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Second Floor
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Most room have set back thermostats. The thermostat controls the pump that forces water through baseboard heaters. All thermostats do not control the boiler operation.
There are several safety and ambient temperature mechanisms used to control the two boilers (north and south)
The "It's Gonna Blow" high water temperature
cutoff prevents the boiler water from exceeding 190 F
The "Maybe it's Summer" control measures outside temperature and prevents the boilers (north and south) from operating when the outside temperature is greater than 65F outside.
The "It's Really Cold" control prevents boiler (north) from firing if the external temperature is greater that 35 F
The two controls for the two outdoor thermostats are mounted on
the ceiling next to the gas meter on the east wall of the boiler
room.
In extremely cold weather, a freeze control system can be activated. The switch is located at the rear of the boiler on the left side of the upper plywood panel.
This system senses outside temperature. If the temperature is below 25 F, a one hour interval "Stoker" timer is activated. Every 30 minutes, the 'Stoker' timer trips a activates relay switch for 1.5 minutes. This relay switch, in turn activated 4 relays that close the circuit on 4 of the zone pumps. The water circulates in the zone for 1.5 minutes. This extra pulse of water in specific freeze sensitive zones insures that the water does not freeze in the pipes. This system does not override or circumvent any other control systems. It is an additional measure of protection.
High wind on cold day: Cold air forced into cracks finds it's way to a pipe which is idle.
Idle zones: The room has been warm for a long time. People leave and the thermostat switches to the set back temperature. The temperature along the exterior wall drops faster than the room temperature and the pipe freezes.
Sun is shining on the outside thermostats located on South Road side of church, just above the foundation. The thermostats think it's summer (see Boiler Temperature Control). This often happens in February when the sun is at just the right angle in the morning.
It's late on Sunday and you can't warm the red classroom. Reason: the church has retained a significant amount of heat because of the Sunday morning activities. The master thermostat in the minister's office is not calling for heat and the boiler water temperature has dropped to 60 F.
The circulator pump has been switched off. A row of switches for the zone pumps is located at the rear of the boiler on the lower plywood panel. The switch may be off. If it happens to be the switch for the Ministers Study, the boiler will also be off.
The clutch for the motor connection to the pump may be broken. If the pump is working and the feed pipe is cold and the boiler is on, then the clutch is broken.
On a mild spring day, when the church is cold inside, the "Maybe it's Summer" sensor may prevent the system from heating. The solution is to temporarily set this sensor to a higher setting. Remember to reset the sensor later or we'll be occasionally heating the church on cool summer nights.
Pipe is frozen. Shut off pump. Shut off return line valve to boiler. Open drain valve. Place bucket under drain valve. Try to heat the pipe or area by heating adjacent room on other zones. Heat area room where pipe is frozen with electric heater. Wait, don't try to rush the process with any open flame device. Try a heat gun.
