Low Water Volume Boiler Vs. Cast Iron Boiler; Determine Radiation Needed Room-By-Room - Keston 50 - GC Installation And Servicing Instructions

WD50/2/1997 Chapter 2 - Boiler Connections
supply to the boiler when the required temperature is reached. Mixing valves are also
available which will mix return water from the system with boiler output water to dilute the
temperature of water transmitted to the distribution system. Mixing valves may create
problems with low flow and high temperatures through the boiler unless care is taken to
design a system which will provide proper flows and will fully load the boiler. Keeping the
boiler's temperature high will prevent the boiler from operating at peak efficiencies.
Systems which maintain boiler temperatures in this way should be avoided.
If only a portion of the boiler's available output is to be used for radiant floor heating a
thermal storage tank will improve the boiler's operation and give adequate control of
temperature for the distribution system. By heating water to be distributed to the radiant
floor zone to the proper temperature in an indirect-fired water heater, full load conditions
will be available to the boiler because the heat exchanger in the tank can be sized to
match the boiler's output. The tank's thermostat can be set at the optimum operating
temperature needed by the distribution system and short-cycling of the boiler will be
prevented. In such insulations it is advisable to calibrate the thermal store's operating
thermostat to become the controlling thermostat of the boiler, ie the thermal store
operating thermostat is always activated to shut off the boiler before the boilers own
thermostat is activated. An insulated thermal storage tank without the heat exchanger may
also be used.
2.13

LOW WATER VOLUME BOILER VS. CAST IRON BOILER

Because of their high water content and mass of metal, cast iron and steel boilers are less
responsive but somewhat more forgiving of design errors. Short-cycling of the
burner on the temperature limit control is less pronounced, though no less detrimental to
operation, because the boiler itself will absorb and radiate a significant amount of heat.
Low water volume boilers respond more quickly to a call for heat, can be made more
compact and lightweight, but must have adequate heat delivery systems to avoid
short-cycling of the burner on the temperature limit control. The heat delivery system's
output must be equal to or greater than the boiler's output to fully load the boiler or
short-cycling will occur.
Likewise, pumping rates of water through low water volume boilers must be maintained so
that water is moved through the boiler fast enough so as not to reach boiling
temperatures. The slower the water moves through the boiler the more heat it will absorb
and the higher the temperatures will rise. Consequently, the pump selected must be
adequate to maintain that critical flow of water.
2.14

DETERMINE RADIATION NEEDED ROOM-BY-ROOM

A radiator or convector's ability to deliver heat is related to the water temperature and the
rate of delivery to the unit. Most systems in the past have been rated at about 80
Higher efficiencies can be gained from a condensing boiler if ratings published at lower
temperatures are used. However, this is not imperative. With normal 80
condensing boiler will still deliver significantly higher efficencies than a non-condensing
boiler. Lower water temperatures in the system tend to increase the efficiency of the
boiler and will help assure that the boiler is subjected to a sufficient load to avoid
short-cycling.
The Keston boilers are capable of temperatures of up to 80
temperature of the return water, the lower the efficiency of the system. This is true of all
boilers, though all non-condensing boiler must be kept at higher temperatures to avoid
condensation in the boiler which destroys such boilers quickly. Materials used in the
Keston are made to withstand the condensates corrosive nature.
Installation & Servicing Instructions
The Keston 50, 60 & 80 Condensing Boilers
Page : 17
o C.
o
C ratings used a
o
C but the higher the