Description

In a ducted air heating system, where air temperature is automatically modulated, there are two performance factors which are of general importance. First, the energy requirement specification must be satisfied, which is dependent on mass-or volumetric-air flow rate and the heated temperature difference. This specification is designed by static energy considerations. The second factor to be considered is the transient behavioral characteristic of the overall closed loop system which includes: temperature sensor, control signal conditioners, water flow rate modulating valve, air heater(s) and air transport system (Fig. 1). These components are all interdependent and must be considered as a total aggregate in the evaluation stage.

Improperly proportioned components may result in temperature hunting, system instability, excessively long transients, etc. This second consideration is of a dynamic nature, and in general is independent of static behavioral aspects. In order to adequately assess this closed loop system behavior, it is first necessary to reliably describe the dynamic behavior of the respective individual components. The intended direction of this paper is toward some of the pertinent dynamic considerations.

Previous investigations by this author, and others, have been directed toward the mathematical modeling and experimental verification of crossflow heat exchanger dynamics (Refs 1, 2, 3, and 4). This component represents the air heater element in the above cited closed loop system aggregate.

Citation: ASHRAE Transactions, Volume 78, Part 2, Nassau, Bahamas

Product Details

Published:

1972

Number of Pages:

7

File Size:

1 file , 500 KB

Product Code(s):

D-NA-2250