Boiler Efficiency speadsheet

[BronYrAur]

Anyone have a good spreadsheet or reference for determining boiler efficiency? I see many threads on the topic but haven't found a good reference or calculator.

My particular situation consists of an old firetube 12psig steam boiler. Hasn't been serviced in a long time and probably runs very inefficiently. The steam goes right to a heat exchanger that makes hot water. The supply water temp setpoint ranges from 120 deg F to 180 deg F depending on the outside air temp. Return temp, however, pretty much consistently comes back around 90 deg.

This looks like a great candidate for condensing boilers or a hybrid system. The client wants to see some ROI numbers, so I am looking efficiencies. Any recommendations would be appreciated.

 

[EnergyProfessional]

Perform a combustion analysis and you will know excess air and flue temperature. those determine efficiency. More excess air and higher flue temp = less efficient.

 

[nglty]

Before we can compare a steam boiler and evaluate for replacement with a condensing boiler, one needs to check steam usage. is there a heat exchanger a the end of the line? do you make DHW with steam? Is the steam used for food warmer? humidification? sterilizers? i.e some steam is lost to the atmosphere, meaning less condensate rerun back to the boiler. Or is this steam boiler purely for heating?
The key number for the steam boiler is the percent condensate return. How much leakage you have in steam traps, how much is evaporated in the process? Anything less than 85/86% condensate return for steam boiler is very inefficient.

 

[GT-EGR]

Without even making it complicated, you might just find that switching to a condensing boiler on its own saves enough on combustion efficiency than even a well combusting and condensation returning steam boiler. Then the rest is just icing on top once you mention the likely less than perfect combustion, loss of condensate, etc.

Unless your ROI isn’t good enough, then it’s always an easy enough calculation if you measure makeup water. Then there’s the combustion analysis as previously mentioned to figure out the real efficiency you previously just assumed was perfect.

It sounds like the steam boiler is an unnecessary step and you should just bring the fire right up a condensing hot water boiler.