Peak loads vs. cold showers: the impact of existing and emerging hot water controllers on load management

Abstract

ABSTRACTElectric Hot Water Cylinders (HWCs) offer considerable Demand Side Management in Aotearoa New Zealand, which can provide load management and increase integration of renewable electricity. In this work, scenario analyses are conducted to simulate the impact on Low Voltage transformer load and demand fulfilment of four HWC controller types: setpoint (the default in Aotearoa New Zealand), ripple, smart-power, and smart-thermostat. All controllers reduce peak electricity demand by 14-34% from setpoint, where 34% is the maximum possible reduction with hot water control. Unmet demand, which indicates insufficient hot water and can lead to negative outcomes such as cold showers, is increased by 120% and 12-69% by ripple and smart-power control, respectively, and decreased by 7-31% by smart-thermostat control. Average thermal losses are 2.25 kWh/day for the setpoint controller, and between 2.20-2.76 kWh/day for other controllers. Smart-power controllers demonstrate demand deferral, shifting peak electricity loads to shoulder loads, while smart-thermostat controllers demonstrate demand deferral and valley filling, shifting peak loads to times of lowest demand and smoothing load distribution. Overall, smart controllers improve load management performance with little-to-no increase in unmet demand or thermal losses. Thus, smart controllers are a viable option for Demand Side Management in Aotearoa New Zealand.Abbreviations and Nomenclature: DHW: Domestic Hot Water; DLC: Dynamic Load Control; DSM: Demand Side Management; EV: Electric Vehicle; GHG: Green House Gas; HV: High Voltage; HWC: Hot Water Cylinder; LDC: Load Duration Curve; LV: Low Voltage; MV: Medium Voltage; NZD: New Zealand Dollar; PV: PhotoVoltaic; TOU: Time Of Use; UD: Unmet Demand; WTP: Willingness To Pay; A: WTP function coefficient; B: WTP function coefficient; Cp: specific heat of water [J/kg/K]; Ctrans: cost imposed by the transformer; HWsuff: ratio of hot water sufficiency; Kloss,h: thermal losses for cylinder h [W/K]; Kmix: thermostatic mixing valve factor; m: WTP function coefficient; Ptotal: transformer power demand [W]; Pcap: transformer capacity [W]; Ph: Household power demand [W].; PHWC: heater element power [W]; Pop: Transformer limit for Type3 controller [W]; QDHW: heat loss from DHW use [W]; Qloss: heat loss from standing losses [W]; th: time horizon [s]; Tamb: ambient temperature [K]; THWC: temperature of the HWC [K]; Tin: water inlet temperature [K]; Tmin: minimum temperature before fulfilment failure; Tout: water outlet temperature [K].; Tset: temperature setpoint of the HWC controller [K]; V˙: flow rate of hot water from the HWC [L/s]; Vavail: available DHW in the HWC [L]; VDHW: volume of hot water draw [L]; VDHW,expected: expected time weighted demand; VDHW,expected,max: maximum expected DHW demand; VHWC: volume of the HWC [L]; wf: time weighting function; ρ: density of water [kg/m3].