In horizontal distribution plants, connection between centralised boiler and individual utility (housing unit), happens by means of a pair of pipes (flow and return).
Therefore, heat consumption can only be measured in one point by installing a heat meter in an appropriate compartment or in the distribution box.
Direct heat metering is based on the use of the following functional blocks:
1. a flowmeter supplying the individual utility, installed on the return piping of the boiler;
2. two temperature probes inserted at area input and output to measure the temperature difference in boiler, between flow and return;
3. a processing unit that processes the signals of the two instruments to calculate the heat consumed by the utility.
The heat meter is essentially a system that integrates the three functional blocks. The processing unit, usually provided with display, is assembled on the flowmeter, whereas the temperature probes connected to it are inserted, respectively, at module input (flow probe providing the temperature value at utility input), and at module output (return probe, often already integrated in the heat meter).
Based on the capacity value and calculating the temperature difference detected by the two probes, with a simple mathematical calculation, the meter is able to determine the instantaneous power consumed by the housing unit and log the progressive consumption:
P
[kW
] = Q
[m3
/h
] ·
ΔT
[°C
]
/ 0.86
where P is the power in kilowatt, Q is the capacity in cubic metres/hour and ∆ the detected temperature difference in degrees centigrade.
By integrating the instantaneous power in time, the value of the energy in kWh consumed by the individual utility is obtained.
In area plants it is normally possible to interrupt the water flow to the utility once the set temperature in the ambient is reached, in which case the flowmeter detects the absence of flow and meters null consumption.
Similarly, a decrease in thermal exchange between heating plant and ambient is recorded by the meter temperature probes, under form of minor difference of temperature measured between flow and return in boiler.
The heat meters are regulated by L.D. 2 February 2007, n.22, that represents the transposition at national level of European Directive 2004/22/EC on measuring instruments, commonly known as "MID". The identification class of the heat meters is MI-004; essential requisites are specified allowing its commercialisation, installation and commissioning at European level. Among them, the CE marking and the M supplementary metrology marking.
MID envisions a transitory period for commercialising non CE-M marked instruments in case, on national territory, these instruments are already regulated by current Standards at time of issuing the Directive. However, it must be remembered that for heat meters in Italy, these transitory dispositions cannot be applied as there is no national regulation before the MID. Therefore, as from March 2007, only MID approved heat meters can be commercialised.
ARCHITECTURE OF A METERING SYSTEM WITH UTILITY MODULES
A system based on heat metering with utility modules envisions a centralised hot water production system (boiler) and a metering module for each housing unit. Regardless of the technical solutions and components the different manufacturers introduce, these modules always envision three basic elements:
1. a DCW volume flow meter
2. a DHW volume flow meter
3. a heat meter
The volume flow metres allow sharing expenses relating to the use of DHW and DCW among the owners, based on real consumption.
Each utility module contains all data for correctly sharing the costs relating to water and energy consumption. It is the task of a purposely appointed person (e.g. property management) to set-out these values to obtain a correct sharing of the costs; it, therefore, becomes fundamental to be able to obtain the values of interest from each individual module. There are different ways of doing this.
Direct reading. The most simple, consists in directly reading the consumption values, module per module. This procedure may be convenient in some cases, when there are only a few number of utilities and the cost of a complex centralised network is not documented. This operation may result expensive in terms of time and, in certain cases "unpleasant", should the boxes be inside the apartments.
Centralisation on M-BUS. Consumption data from each module is transmitted to a central collection unit (commonly called "concentrator"), using the M-BUS communication protocol. It is then possible to download data on PC, through opportune devices.
Centralisation via radio. In this case, radiofrequency signals are given by each module, collected by receiver antennas and transmitted to a central unit for data collection. In this case also it is possible to download the consumption data in different ways.
IVAR SPA proposes a wide range of heat metering to satisfy all possible engineering requirements.
The individual modules are supplied with TEMPLATE blocks instead of meters, making it necessary to complete the module by ordering the relative electronic devices kits, according to the tables below.
The offer has been structured in four sizes (Kv = 2.25 – 2.75 – 3.50 - 7), depending on the flow rate features (and, therefore, power) requested by the plant project. More in detail, the first two class of sizes (Kv = 2.25 – 2.75) belong to the family of modules EQUIMETER, respectively EQM 1 and EQM 2, whereas, the other two higher classes, belong to that of the MC1, MC2 and MC4 metering modules.
Each size has a range of variations, available with or without wall fitted box:
The range has also been completed with two metering modules for MC3A and MC3B domestic use only, with possible variations.
With regard to electronics, the offer has been divided into two main kits:
All available in direct reading, M-BUS or RADIO version.
In addition to standard metering devices, IVAR is able to supply two alternative systems: the S system and the K system. The codes of the equivalent kits are obtained by eliminating the letter Q and adding the S or the K.
The K system is particularly innovative: it is an OPEN system where the heat meter can be adapted at any moment to any communication system (M-BUS, RADIO, impulsive) by means of adequate outdoor adapters communicating with the optical interface equipped on the meter.
A summary table with the proposed kits and the three different system alternatives can be found after the price list.
INSULATION SHELL: with regard to thermal insulation of the heat metering modules, it is specified that:
Note: the domestic water and cold water metering devices in the following tables are characterised by Qn = 1.5 m3/h or 2.5 m3/h with respective lengths of 110 mm and 130 mm. An exception is given by the direct reading devices having nominal capacities equal to 2.5 m3/h and 4.0 m3/h with similar lengths equal to 110 mm and 130 mm.