DOE-2 Reference Manual Version 2.1 - DOE2.com

5. SYSTEM Control Strategya. General Discussion for all SYSTEM-TYPEsThe following information describes how DOE-2 simulates the differentcontrol strategies for each SYSTEM-TYPE. The information in this subsectionapplies to all strategies and all SYSTEM-TYPEs (it is inserteOlhere in anattempt to eliminate unnecessary repetition).The importance of understanding how an HVAC system works cannot be overemphasized. Minor changes in the system control strategy can often have largeeffects in energy consumption and conservation. Often these energy conservingchanges involve a minimum of expense to employ. Examples of such changesinclude using temperature setback, resetting the economizer limit temperature,reducing excessive outside ventilation air, resetting hot and cold decktemperatures, and employing better fan schedules. However, to employ theproper changes in the system, the user must first understand how his system issimulated by DOE-2. That is the purpose of the following discussions.Occasionally, the user will note that there are slight differences betweenthe simulation methodology and the "real world of hardware". That is to say,although the computer simulation will be thermodynamically close, it would beimpossible to purchase equipment that would exactly duplicate the simulationaction. This is true of most computer models and the user should not be undulyconcerned.Some control strategy keywords are appropriate only at the ZONE level,while others are appropriate only at the SYSTEM level. Still others are appropriateat both levels. If a keyword, which is appropriate at both levels, isspecified only at the SYSTEM level it will apply to all ZONEs served by theSYSTEM. If a keyword, which is appropriate at both levels, is specified bothat the SYSTEM level and at the ZONE level, the specification made at the ZONElevel will take precedence over the SYSTEM level specification.In the following discussions, the term constant volume flow refers to thevolume of supply air entering the ZONE for all hours of the simulation. Likewise,variable volume flow, refers to the volume of supply air entering theZONE; however, in this case, the quantity of air may vary from one simulationhour to the next (but during anyone simulation hour the volume remains constant).Likewise, in the following discussions, constant temperature andvariable temperature have analogous definitions.Also, the user will note in the following discussions that "heatingsources" are generally referred to as preheat coils, main heating coils, orzone coils. The same is true for "cooling sources". In DOE-2 heating andcooling can be accomplished with other energy sources other than fluids (gas,electricity, solar, heat pumps, etc.) "Heating coils" and "cooling coils" areused, in the following discussions, in the generic sense.Throughout this section on SYSTEM Control Strategy, keywords areidentified as belonging to certain subcommands. The user is reminded herethat any keyword that belongs to a subcommand (i.e., ZONE-AIR andZONE-CONTROL) can also be entered in the parent command (i.e., ZONE). Thesame is true for SYSTEM subcommands and the SYSTEM command.IV.105 (Revised 5/81)