background image

2. Introduction 

 
One of the elements in both Natural Gas 
and Propane is hydrogen. A gas burning 
appliance mixes the gas with air and during 
the combustion process hydrogen and 
oxygen combine together and produce heat 
(143,100kJ/kg) and water vapour (H

2

O). 

 
For every kg of hydrogen burned 9kg of 
water vapour is produced.   The 
temperature in the heat exchanger of a 
boiler can reach 1400

0

C.   The water vapour 

produced is so hot it turns into superheated 
steam.  
 

2.1 

The Condensing Process 

This superheated steam contains both 
sensible (available heat) and latent heat 
(heat locked up in the flue gases).  A 
conventional boiler will recover some of the 
sensible heat by passing these hot gases 
over a heat exchanger.    
 
The heat exchanger in non-condensing 
boilers is generally made of cast iron and 
cools the gases to between 250

0

C and 

350

0

C.   A conventional boiler does not 

recover any of the latent heat and this 
energy is simply lost to the atmosphere 
through a metal flue.  These flue gases are 
extremely hot and the lost energy wasted 
can equate to up to half of the annual 
running costs. 
 
A simple condensing boiler will however 
extract more of the sensible heat and some 
of the latent heat by cooling the flue gases 
down to below 100

0

C. 

 
When a condensing boiler is operating in its 
most efficient manner flue gas temperatures 
of around 50

0

C will be achieved and the 

boiler will now start to condense the flue 
gases.  The superheated steam is cooled to 
its dew point, typically around 55

0

C the flue 

gases give up their latent heat to the boiler 
and condense out.   
 
The critical factor that ensures maximum 
efficiency from a condensing boiler is the    
water return temperature. The water return 
temperature determines whether the boiler 
operates in condensing mode, which in turn 
controls the boilers efficiency. 

To sum up, with water return temperature of 
55

0

C or less, the latent heat is condensed 

out of the flue gases.    
 
A typical, non-condensing, central heating 
system is designed with a water flow 
temperature of 80

0

C and a return water 

differential of 10

0

C.  This design differential 

is critical.   
 
System designs had to incorporate high 
return temperatures (typically 70

0

C) to stop 

any unwanted condensing of the flue gases.    
The flue gases leaving a conventional boiler 
have to be discharged very hot for the 
following reasons. 
 
To propel the flue gases up a chimney or 
through a flue they have to be discharged 
hot to give them buoyancy and enough 
thermal lift to overcome the flues natural 
resistance.

 

 
If the flue gases are not hot enough the 
effectiveness of the flue system is reduced 
and harmful by products of combustion 
could enter the building via the appliance or 
its flue.

 

 
A conventional boiler has to discharge the 
flue gases hot to prevent any unwanted 
condensing.  If the flue gases are not kept 
hot enough they will condense allowing 
water to run back down the flue and into the 
boiler. 

 

Clearly this has to be avoided. Heat 
exchangers made of cast iron, or boiler 
designs not equipped to discharge this 
water would suffer imminent failure. 

 

 
The flue gas discharge from conventional 
boilers has to be maintained at high 
temperatures.  
 
Questions you might be asking yourself now 
might include:  

Question?

  Why were such inefficient 

appliances designed?    

 
Answer:

 

 

 

Fossil fuels were 

cheap and the environmental 
consequences of burning and wasting so 
much fuel were not fully appreciated.  
 

 

EC 25 Compact Technical Manual page 

5

   

Summary of Contents for EC 25 COMPACT

Page 1: ...eco hometec Variable Controlled Output VCO Solar Compatible jjjjj Gas Condensing Boilers EC 25 COMPACT T TE EC CH HN NI IC CA AL L M MA AN NU UA AL L...

Page 2: ...ls EC25CompactTechnicalManual021099 doc 30 June 2002 eco hometec has a policy of continuous improvement and reserves the right to change any specification without notice Your statutory rights are not...

Page 3: ...ial Connection 21 11 2 8 1 5 Frost protection 21 11 3 Weather compensation 21 12 Hot water output 22 12 1 Combi Type S Tap boiler 22 12 2 Pump operation 22 12 3 Hot Water Cylinder 22 13 Safety devices...

Page 4: ...ng burner Energy saving modulating pump Energy saving modulating system water temperature Corrosion free PPS plastic flue tubes and fittings offering ease of siting Data logging via PC for analysing p...

Page 5: ...from a condensing boiler is the water return temperature The water return temperature determines whether the boiler operates in condensing mode which in turn controls the boilers efficiency To sum up...

Page 6: ...existing system with an 80 700 C design But by lowering the water return temperature condensing boilers are capable of achieving efficiencies up to 98 How then can we lower the return water temperatu...

Page 7: ...r passage these hot gases are used to preheat both the return water to the boiler and the incoming combustion air thus ensuring that all of the available energy is used as efficiently as possible 3 2...

Page 8: ...ts 4 x 15mm connections it offers a low temperature output typically 55O C for under floor heating or a fixed variable temperature output for connection to radiators Despite the low boiler flow temper...

Page 9: ...Figure 1 Solar heating EC25 S Type Combi Hydraulic system design when installed with solar heating EC 25 Compact Technical Manual page 9...

Page 10: ...of Flue Gases 00 C 52 Flue Gas Temp 80 600 C Amb 200 C 00 C 70o C Maximum Flue Resistance Pa 185 pH value of condensate water PH 4 5 5 Maximum Flow Temperature 00 C 90 Min Max filling pressure bar 1...

Page 11: ...ct ti io on n V Va al lu ue es s Min Max Gas Pressure mbar 20 25 Maximum Input Rate Natural Gas H HS Types m h3 2 58 Maximum Input Rate Natural Gas S Types m h3 2 95 Electrical Supply VAC 230 Power C...

Page 12: ...F Fi ig gu ur re e 2 2 C Co om mp po on ne en nt t L Lo oc ca at ti io on ns s Page 12 ECO HOMETEC UK LTD...

Page 13: ...n tray 10 Gas valve 11 Fan 12 Venturi tube 13 Water pressure sensor 14 Supply sensor 15 Return sensor 16 Safety device 17 Bleed valve 18 Hot water sensor 19 Exhaust gas sensor 20 Type plate 21 Condens...

Page 14: ...tion to a PC For more details please contact the eco hometec technical department T Ta ab bl le e 8 8 E Ex xt tr ra a I It te em ms s a an nd d a ac cc ce es ss so or ri ie es s All Types All Types Al...

Page 15: ...it is important to consider at the first fixing stage the order you arrange the pipe work and if applicable any cable trunking Figure 3 shows the order in which to fix the pipe work 7 2 Connections 1...

Page 16: ...F Fi ig gu ur re e 4 4 O Ov ve er ra al ll l D Di im me en ns si io on ns s Page 16 ECO HOMETEC UK LTD...

Page 17: ...d Flue Kit 80 125 PPS White Galvanised 90 degree elbow 80 125 PPS White Galvanised 45 degree elbow 80 125 1000mm length PPS White Galvanised Concentric Flue 80 125 500mm length PPS White Galvanised Co...

Page 18: ...hometec for further advice Figure 6 Vertical Flue Application 8 4 Modular installations For multiple boiler modular installations eco hometec supply a range of larger diameter flues Sizes are availabl...

Page 19: ...surance that the joints have been fully pushed home the seal rings and make ends of tubes and fittings should be lightly lubricated with silicone grease Additional 80 125mm concentric flues tubes and...

Page 20: ...be 32mm The existing drainage system should be corrosion resistant 8 6 System By Pass The boiler is designed to operate at a minimum flow rate If zone valves are fitted to all the heating circuits the...

Page 21: ...rature detected by the supply sensor falls below 8 C the pump will be switched on and will circulate water through the central heating circuit If the temperature detected by the supply sensor falls be...

Page 22: ...s and the pre ignition phase begins At the end of the pre ignition phase the system pressure is measured again The following situations are possible Pressure difference 0 06 bar 1 Air in the appliance...

Page 23: ...the control system will block further operation with a flashing 2 on the status display and the supply temperature on the temperature display Once in every two hours the difference between supply and...

Page 24: ...est return water temperatures and will ensure the condensing boiler will operate more efficiently The EC25 may be safely fitted to systems using a high temperature thermal store however we bring to yo...

Page 25: ...lower heat losses due to smaller diameter pipework and should result in installation savings with reduced costs for pipe fittings pipe insulation and installation costs 15 4 Control of Circuits The re...

Page 26: ...hometec are fitted with Variable Controlled Output eco hometec Unit 11E Carcroft Enterprise Park Carcroft Doncaster DN6 8DD Tel 01302 722266 Fax 01302 728634 http www eco hometec co uk e mail sales ec...

Reviews: