General Instruction - Keston C90 Installation And Servicing Instrucnion

WD352/0/2003 Chapter 1 : General Instruction
1.1 DESCRIPTION
The Keston C90 and C110 are unique in concept and design. They comprise two high
efficiency stainless steel heat exchangers coupled with low emissions burners to deliver
ultra high efficiency condensing mode operation within a compact wall hung cabinet. The
unit automatically adjusts gas and air rate according to demand to give an output in the
range of 22kW to 90kW (C90) and 25kW to 110kW (C110). The integral Grundfos pumps
are automatically controlled to best match water flow rate to heat output & further increase
appliance efficiency. In addition, the boilers feature an optional connection for an outside
sensor to enable the boilers inbuilt weather compensation option. Separate inputs are
provided for hot water and central heating demand signals to enable different temperature
levels to be set (ideal for underfloor heating systems). The boiler features two sets of flow
and return tappings to enable these two temperature levels to be supplied simultaneously.
Common applications for this technology are weather compensated heating in conjunction
with high temperature flow for DHW production. While the application for which the C90
and C110 were designed is the same as those which other boilers are used, the Keston
C90 and C110 have the added advantage of very high efficiency, and small diameter
plastic flue which can be extended up to 30m metres horizontally or vertically.
The Keston C90 and C110 uses a variable speed combustion blowers to deliver a premix
of gas and air to a downward firing burners in high efficiency, single pass heat
exchangers. The flue system is room sealed and fan powered. The ignition is direct spark
and fully automatic. The boiler housing is not waterproof and should be installed in a
position where it will always be dry. Combustion air is drawn from the cabinet which is
connected to outside atmosphere via a plastic intake pipe. The cabinet therefore remains
under negative pressure at all times the boiler is operating.
The boiler is suitable for connection to open vented or, preferably, sealed systems.
The boiler has two heat exchangers. They are made from highly corrosion resistant
stainless steel in corrugated pipe form which provides massive surface area within a
compact dimension. The hot combustion gases from the down firing burner pass around
the stainless steel pipes imparting heat into the system water. The integral variable speed
Grundfos pumps within the appliance cabinet ensures the heat exchanger receives
correct water flow when firing. The C90 and C110 are not high water content boilers and
do not contain the metal mass, or water volume, of a cast iron or steel boiler. The boiler is
of low mass and low water content and therefore responds faster when there is a call for
heat. The C90 and C110 feature full user diagnostics, integral frost protection function,
automatic pump and fan exercise in periods of inactivity, anti cycle control, dry fire
protection and connections for remote lockout and run monitoring (optional accessory).
1.2 BOILER SCHEMATIC
Air is drawn into the boiler through a 100 mm Keston Composite plastic pipe. Gas is
mixed with combustion air at the inlet to the fan. The gas flow is automatically regulated by
the gas valve according to the air flow generated by the fan. The gas and air are
thoroughly mixed in the blower and fed into the burner located at the top end of the heat
exchanger module. The gas and air mixture is ignited by a direct spark ignition control
system and burns with a blue flame just off the surface of the burner. As the hot products
of combustion pass downwards, they are cooled by exchanging heat with the circulating
water which enters the heat exchanger at the bottom of the heat exchanger. The optimum
heat input is detected by monitoring flow and return temperatures and is adjusted by
controlling the speed of the fan. The optimum pump speed is also detected and
automatically selected by the boiler.
When the return water temperature is below 55
combustion products will condense inside the heat exchanger, thus increasing the boiler
efficiency further by releasing the latent heat of condensation. This condensate falls to the
bottom of the heat exchanger where it is separated from the flue gases and exits from the
Installation & Servicing Instructions

1. GENERAL INSTRUCTION

The Keston C90 & C110
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C, part of the water vapour in the
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