[BLDG-SIM] boiler

Fred Porter fporter at archenergy.com
Thu Jun 16 05:29:22 PDT 2005

Good thing to check!
The PS-C heat load divided by the PS-C fuel use is the annual 
boiler-only efficiency that DOE-2.2 has calculated:
1. starting from the 84% steady-state, full-load, thermal efficiency (or 
combustion efficiency if you input boiler shell losses separately),
2. considering any other inputs to the boiler command or the default 
boiler values,
3. using the (much less than full load) load distribution over the year,
4. applying the DOE2.2 boiler algorithms.

The resulting "almost two-thirds" annual efficiency from 84% 
steady-state, would be typical of, or better than, the annual efficiency 
of a big, old, boiler.

The boiler algorithms and default inputs and curves need to be used with 
caution. Check the "dictionary" and some old posts in the listserv 
archive; in particular:  

The PS-C heating load should equal the HW loop load, which is the sum of 
loads from the systems, and the load from the loop losses, if any are 
defined. The "coil loads" on the HW loop should be the loads from the 
systems (The system loads include outside air, overcooling & reheating, 
and the temperature setpoint schedule), and any process loads defined. 
The loads in loads are calculated at a constant temperature defined in 
the space command, and don't include any system effects. They do not 
apply to this issue.

Vämshi Goojè wrote:

> Hi-
> In the PS-C report (sim file), the annual heating load for the boiler 
> is almost two-third the annual fuel use (in MBtu).
> I'm assuming that ventilation load is the difference between the 
> heating loads from PS-C and LS-F, so PS-C should have ventilation 
> included. Correct me if 'm wrong.
> The boiler heat load is 1940 MBTU and the Fuel use is 3100 MBTU 
> (PS-C). Applying, 84% boiler efficiency to heat load should give me 
> 2308 MBTU (i.e., 1940* 1.19).
> So where am I getting that extra 800 MBTU from?
> Any feedback appreciated.
> -- 
> Vämshi Goojè

Fred W. Porter
Senior Engineer
Architectural Energy Corp.
2540 Frontier Ave. Suite 201
Boulder CO 80301

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