# Smart Energy Meters for Smart Grids, an Internet of Things Perspective
## 2 Sensing Techniques
### Heat Meters  
The thermal energy or heat is measured by integrating the flow of the liquid with the differential temperature of the fluid that supplies or removes heat. A basic sensing of the heat supplied or removed is obtained by multiplying the fluidic mass flow by the specific heat and the temperature difference between the supplied and the return fluid. Heat supply systems use either steam or some other fluid, with fluidic systems becoming more commonplace. The temperature difference is measured using a temperature sensor, while the flow is measured using either a dynamic or a static technique. Dynamic techniques use a moving mechanical part such as an impeller or a turbine to measure the mass flow, whereas static meters use electronic techniques, with the most common being ultrasonic and magnetic induction. Heat flux meters are also becoming commonplace in modern building systems to measure the heat flow across the insulation for better control of environmental temperature. The heat meters have been extensively researched and designed. The earliest works on measuring latent heat using mechanical flow meters, such as impellers and rotary wing sensors, are carried out in [47; 48; 49]. The ultrasonic meter for measuring flow in heat meters is reported in [50]; it corrected the errors induced due to temperature variations, resulting in increased dynamic range for heat flux measurements. Furthermore, in [51] the authors proposed a method to increase the range of heat meters. Thin film-based heat flux meters are discussed in [52]. The parametric study of different aspects of the design and operation of heat meters is also discussed in the literature. Ref. [53] carried out a theoretical study  
Figure 3: Smart meter as a physical node consists of sensing technique, computation platform, and communication technology. Computation platform consists of hardware, such as single board computers, microcontrollers, and system on chip and software such as API tools. Communication technology consists of data communication and middleware protocols. on the conditions of the minimum error of the heat flux meters. Ref. [50] discusses the design trade-off of small thickness/width ratios for the heat flux meters. Ref. [54] reviews the effect of installation conditions on the working of heat flux meters. Ref. [55] reviews the temperature-sensing techniques in heat flow measurements. Refs. [56; 57] review the techniques for heat flux measurement with regard to the theoretical and developmental aspects for different applications. These reviews are somewhat dated, but the techniques detailed by them are still pertinent and are still being used in the heat flow measurements. Based on the solid theoretical framework, there is an abundance of practically built heat flow meters, ranging from simple ones to electronically integrating meters. Ref. [58] designed a simple heat flow meter using off-the-shelf electronics component. Though the efficiency has not been compared to commercially available solutions, the meter is functioning, cheap, and reliable. Ref. [59] added communication capability for automated reading. Ref. [60] designed a heat exchanger-based heat flow meter that uses mechanical parts in static configuration. Refs. [61; 62] use electronic circuits for the flow calculation and compensation of related perturbations, increasing the reliability of the electronics-based systems. Ref. [63] uses a non-magnetic electronic flow calculation technique for heat meters for increased robustness against perturbations in flow, liquid compression, and rapid temperature changes. Heat flux meter designs are reported in [64], which uses silicon to measure heat flux, and [65], which implements a thin film-based heat flux meter. With the existence of strong theoretical literature, varied implementations, and real-world usage, several standards have been developed for heat metering, such as those in [66; 67; 68; 69].