Some manufacturers have addressed these problems through incorporation of a small buffer tank within the TWH.
Pertaining to short-term residential hot water demand and its impact on TWH performance, prior and current research has primarily focused on characterizing the nature of hot water demand, the impact of nonstandard draw patterns on the daily delivered efficiency of TWHs, and arriving at a test model of hot water draw patterns composed of both short and low flow and long and high flow draws that are consistent with field test findings.
92 derating factor (the derating factor reduces the EF due to as-installed efficiency loss) in the estimation of TWH efficiency through their energy simulation tool, EnergyGauge[R].
The stored energy within the heat exchanger could not be neglected, thus the thermal capacitance of the TWH was important to transient performance (Glanville 2010).
Short-term testing includes a matrix of short-term tests that (a) define critical physical parameters of the TWH, such as the product of the heat transfer coefficient and heat exchanger area (UA) of the heat exchanger, (b) investigate startup behavior for intermittent (on/off) draws with varying standby durations, and (c) a two shower test, simulating step changes in hot water demand and evaluating outlet temperature control.
TWH testing is intended to (a) provide data sets for the validation of modeling tools and (b) investigate the nature of startup delays and other short-term performance phenomena.
As a consequence, we use a control method that is based on a model for the TWH, commonly referred to as model predictive control.
TWH modeling and validation: We created and tuned a dynamic model of the TWH, accounting for the thermal mass of the components of the tubular heater and heat exchange with the environment, in addition to the heat required to heat the water flow.
A high-fidelity model of the physical process--in our case the TWH--has the benefit that the TWH configuration (e.
For problems involving control system design, a quasi-steady-state approach fails to capture the dynamics that describe the heat transfer problem, so the TWH system needs to be described dynamically.
This assumption allows us to sketch a modified zoning schematic for one chamber of the TWH, as shown in Figure 3.
The heat source term is multiplied with a heat input efficiency [eta] to account for the fact that not all of the heat delivered to the TWH ends up in the water stream (i.