Laboratory exercise 3: Condensing water heater

Transcription

1 Chapter 1 Laboratory exercise 3: Condensing water heater The laboratory exercise Condensing water heater is placed on the Faculty of Mechanical Engineering in the Laboratory for Water and Turbine Machinery. 1.1 Introduction Condensing boilers are water heaters fuelled by gas or oil. They achieve high efficiency (typically greater than 90% on the higher heating value) by condensing water vapour in the exhaust gases and so recovering its latent heat of vaporisation, which would otherwise have been wasted. This condensed vapour leaves the system in liquid form, via a drain. In domestic installations, potable water heated for uses other than space heating is also called domestic hot water (DHW). In a conventional boiler, fuel is burned and produced hot gases pass through a heat exchanger where much of their heat is transferred to water, thus raising the water s temperature. One of the hot gases produced in the combustion process is water vapour (steam), which arises from burning the hydrogen content of the fuel. A condensing boiler extracts additional heat from the waste gases by condensing this water vapour to liquid water, thus recovering its latent heat of vaporization. A typical increase of efficiency can be as much as 10-12%. While the effectiveness of the condensing process varies depending on the temperature of the water returning to the boiler, it is always at least as efficient as a non-condensing boiler. This has also had the benefit of providing the energy for the flue system as the expelled combustion gases are usually below 100 C and as such, have a density close to air, with little buoyancy. The combustion fan helps to pump exhaust gas to the outside. Within the laboratory exercise students will learn about the condensing gas heater operation. 1

2 CHAPTER 1. LABORATORY EXERCISE 3: CONDENSING WATER HEATER 2 For the exercise a standard domestic gas heater Ferroli Econcept 35C is provided. Caution! The following exercise includes operation with natural gas, high temperature exhaust, high temperature water and electricity, thus extreme caution is requested. 1.2 Experimental set-up The experimental set-up consists of the domestic condensing gas heater (Fig 1.1), where the following operating parameters are monitored: inlet water temperature, outlet water temperature, water flowrate, exhaust gas temperature, exhaust gas humidity, exhaust gas flowrate, ambient temperature, ambient humidity, electrical consumption, natural gas consumption. The listed parameters are monitored via National Instrument Field Point DAQ device (Fig 1.2), except gas consumption is monitored by analog gas counter and electrical consumption is monitored by Norma For the exhaust analysis an additional exhaust analyser is provided, which can measure O 2 and CO level. Before the startup, the heater must be connected to the water pipeline and the water flow must be established through the heater. The drain pipe must be put in an external reservoir, where the drain water is collected. The exhaust pipe must be pointed outside through the window. The startup of the heater is executed via command buttons on the gas furnace s front panel. The

3 CHAPTER 1. LABORATORY EXERCISE 3: CONDENSING WATER HEATER 3 Figure 1.1: Experimental set-up in the laboratory. Figure 1.2: NI data acquisition measuring system (FieldPoint). furnace has two separated water circuits, one for the household central heating system (which is in our case eliminated via short cut connection), and the other for domestic hot water (which in our case is used for the measurements). On the control panel, the summer regime must be used, which automatically eliminates the priority of the household heating system circuit. After the startup of the gas heater 2-3 operating points must be selected (flowrate and output temperature can be set). The furnace has a small volume reservoir installed, which serves as a hot water collector to provide a constant hot water supply. In case of setting an operating point with a too low hot water consumption, the gas heater can automatically stops during the measurements. Operating points must be chosen to provide a constant gas burning for 5-10 minutes.

4 CHAPTER 1. LABORATORY EXERCISE 3: CONDENSING WATER HEATER 4 Figure 1.3: Plumbing scheme for Ferroli Econcept 35C.

5 CHAPTER 1. LABORATORY EXERCISE 3: CONDENSING WATER HEATER Student task list 1. Connect all the necessary data acquisition equipment, 2. Measure all the necessary parameters, 3. Draw experimental set-up scheme, 4. Draw all the energy flows in the system, 5. Define energy balance equation, 6. Calculate the efficiency of the water heater, 7. Analyse the exhaust fumes, 8. Define the approximately composition of the natural gas (find it on the internet), 9. Write a report about the laboratory exercise. Comments about the measurements and the results must be included Additional work For grade 10, student can perform the following tasks: Analyse the comparison between the natural gas, biogas and liquefied petroleum gas. Write about their general composition, use, combustion... Additional work can contain maximum 3 A4 pages of material.