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rev. 2008-11-25

Existing Conditions

Two copper-tube atmospheric boilers deliver hot water to the heating system.  The boiler temperature is presently reset with the outdoor air temperature, although the temperature is barely reset.  The existing plant is old and was designed with low capital cost in mind.  This type of boiler is a low first cost item, but is expensive in long-term energy consumption.  The low water volume in the boiler results in very short firing cycles and resulting startup inefficiencies.  Relatively thin insulation and the atmospheric flue contribute to very high standby losses.  The overall efficiency on a seasonal basis is around 65%.

Retrofit Conditions

It is recommended that a new high efficiency forced draft boiler be installed and controlled as the lead boiler, to carry the base load in winter and the entire load in the spring and fall.  We recommend vertical coil tube designs from Patterson-Kelley, Lochinvar, or RBI because:

We recommend removing one of the existing boilers and re-piping the second existing boiler to reduce standby losses.

A proposed schematic is included in Appendix E: Savings Opportunities.

At the same time, the piping should be reconfigured to assure the highest possible operating efficiency under all load conditions, and to ensure that the selected boilers will always be operating under the right flow and temperature conditions for longest life expectancy.  Piping layout is a critical aspect of a new plant that should not be ignored when new boilers are installed.

<Given the age of the existing plant, aging auxiliary equipment such as pumps and valves should be replaced at the same time that the piping is reworked and the new boilers are installed.  Otherwise those points of maintenance and potential failure will remain.>

Further Benefits

 

 

Application Details

In facilities that operate for extended periods with low heating loads, install a small, efficient lead boiler.

Appropriate for many boiler plants.  In addition to saving energy, it may provide opportunities for reducing maintenance and labour costs, and for using less expensive energy sources.  In new facilities, this is basic good design that can save money

Issues and Concerns

 

References

 

 

 

Analysis

(((From CBC Calgary)))

The first step is to establish how the load is distributed for the winter, and for the base load (if any)

Column C is the rated INPUT of the heating equipment

Column D indicates whether or not any equipment is used to its full extent at the peak heating moment

Column E = D x C

Column F = E ÷ E(total)

Column G = F x Total Winter Consumption

Column H = ___? I would expect it to equal near 100%. 

Column I = H x C

Column J = I x I(Total Base Load)

Column K = J x Total Base Consumption

 

Next, the Bin Method is used to calculate the existing conditions, the retrofit conditions, and the savings.

 

Savings can be realized in two ways:

First, with an existing system, the boiler supply water temperature can be controlled to decrease as the outside air increases.  This example starts to decrease from 180 F at -22ºC (-7.5ºF) to 120ºF at the base HDD temperature.  It decreases at 1.66ºF per 5ºF.

Second, a new heating plant and a new DHW system are included in this example.  The Condensing boiler achieves UP TO 92% efficiency, and looses 1% per 5ºF.  The DHW system remains constant.

The new DHW system is calculated as (Existing DHW Consumption x DHW Efficiency ÷ Retrofit DHW Efficiency)

The new heating plant is calculated as (Existing Boiler Consumption x Boiler Efficiency ÷ Retrofit Boiler Efficiency)

Existing - New = Savings

 

 

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