Tankless water heater - also called instantaneous , ongoing stream , inline , flash , on demand , or water heater instant-on is a water heater that instantly heats water as it flows through the device, and does not store any water internally except for what in the exchanger coil hot. Copper heat exchangers are preferred in this unit due to their high thermal conductivity and ease of fabrication.
Tankless heaters can be installed throughout households at more than one point of use (POU), away from central water heaters, or larger centralized models may still be used to provide all the hot water requirements for the entire house. The main advantage of a tankless water heater is the abundant continuous flow of hot water (compared to the continuously heated hot water stream from the conventional tank water heater), and potential energy savings in some conditions. The main disadvantage of this system is the high initial cost (equipment and installation).
Video Tankless water heating
Operation
The heater is usually turned off, but it is equipped with a flow sensor that activates it when water flows through it. A negative feedback is used to bring water to the target temperature. Water circulates through a copper heat exchanger and is warmed by a gas or electric heater. Since there is no limited hot water tank that can run out, the heater provides a continuous supply. To protect the unit in acidic environments, durable coatings or other surface treatments are available. The acid-resistant layer is able to withstand temperatures of 1000 ° C.
Maps Tankless water heating
Combo boiler
Combination or combi boilers combine central heating with domestic hot water (DHW) in one device. When DHW is used, the combination boiler stops pumping water to the heating circuit and diverts all boiler power to DHW heating. Some combis have small internal water storage vessels that combine energy from stored water and gas or oil stoves to provide faster DHW in the taps or to increase the DHW flow rate.
Combined boilers are rated according to the DHW flow rate. The kW rating for domestic units is usually 24 kW to 54 kW, giving an estimated flow rate of 9 to 23 liters (2.4 to 6.1 US gal) per minute. Larger units are used in commercial and institutional applications, or for multi-unit dwellings. The high flow rate model can simultaneously supply two bathrooms.
Combined boilers require less space than conventional tanked systems, and are significantly cheaper to install, because water and pipe tanks and associated controls are not required. Another advantage is that more than one unit can be used to provide separate heating zones or multiple bathrooms, giving greater time and temperature control. For example, one 'combi' might supply a lower floor heating system and the other upstairs, duplication guarding against heating loss and DHW in case one unit fails, provided both systems are interconnected with the valve (usually closed).
Combined boilers are very popular in Europe where market share in some countries exceeds 70%, with the projected increase in the UK to 78% by 2020. This trend is partly due to the social trend toward more but smaller households and the trend continues to increase towards physically smaller and often high-density housing.
The shortcomings of the combination system include lower water flow rates than storage cylinders especially in winter, and the requirement that the overall power rating should be in line with peak warming needs. While 'on demand' water heating increases energy efficiency, the volume of water available at any given moment is limited, the 'combi' design must be matched to the water supply pressure.
(Some designs originating from before the turn of the century, especially the Ideal Sprint, are included as standard flow regulators that allow the same model to function efficiently in the main and low water supply areas, thus accommodating the wide variety of supply pressures often encountered in similar urban settings such as Greater London.)
While the combination boiler has a more moving portion and is thus widely considered less reliable than the tank system, the twin trends on replacement of parts based on predetermined design life and replaceable digital controls for 'traditional' systems have greatly eroded this distinction.
Types of point-of-use (POU) without tank
Tankless point-of-use water heating (POU) is located right where the water is used, so the water is almost instantly hot, which reduces water drainage. Heaters without POU tanks can also save more energy than centralized centralized water heating, as there is no hot water left in the long supply pipe after the flow is turned off. However, POU-free water heaters are often installed in combination with central water heaters, as the previous type is usually limited to below 6 liters/minute (1.5 US gallons/min), which is sufficient for light use only. In many situations, the initial cost of buying and installing a separate POU heater for each kitchen, laundry room, bathroom, and sink can be greater than the money saved in water and energy bills. In the US, POU water heaters are almost always electricity, and electricity is often much more expensive than natural gas or propane (when the last available fuel).
In recent years, higher-capacity tankless heaters have become more widely available, but their feasibility may still be limited by the infrastructure's ability to provide energy (maximum electric amperes or gas flow rates) fast enough to meet peak hot water demand. In the past, tank type water heaters have been used to compensate for lower energy delivery capacity, and they are still useful when energy infrastructure may have limited capacity, often reflected in peak energy demand costs.
In theory, tankless heaters can always be more efficient than storage tanks of water heaters. In both types of installations (centralized and POU), the absence of energy-saving tanks compared to conventional tank type water heaters, which must reheat water in the tank due to cold when waiting is used (this is called "standby" losses.) In some installations, the energy lost by the heater located inside the building only helps to heat the occupied space.This is true for the electric unit, but for the gas unit, some of this lost energy exits through the exhaust pit.However, the building must be cooled to keep the temperature convenient, the heat lost from the hot water tank located in the conditioned room should be disposed of by the air conditioning system, thus requiring greater cooling capacity and energy use.
With any type of central water heater, any cold water standing in the pipe between the heater and the point of use is discharged to the drain when hot water flows from the heater. This waste of water can be avoided if the recirculator pump is installed, but with the energy cost to run the pump, plus the energy to reheat water recirculated through the pipe. Some recirculation systems reduce the standby losses by only operating at certain times - shutting down late at night, for example. It saves energy at the expense of greater system complexity.
Water heater without hybrid tanks
Hybrid water heater is a water heating system that integrates the technological properties of tank type water heaters and tankless water heaters.
The hybrid water heater maintains consistent water pressure and hot water supply in some hot water applications, and like its tankless cousin, this hybrid is efficient and can supply continuous hot water flow on demand.
The hybrid approach is designed to eliminate common flaws from other technologies. For example, hybrids are enabled by either thermostat (similar to tanked) or flow (similar to tankless).
Hybrids have small storage tanks that dampen cold water coming in. This means hybrids just need to raise the water temperature from warm to hot compared to the tank that must raise the cold water completely into heat. The defining characteristics of "hybrid water heaters" are:
- Combination tank water flow and tankless water heater efficiency
- Small storage water containers installed as part of a heat exchanger (usually between two gallons to 20 gallons)
- Double activation: flow controller and thermostat control
Hybrid water heater can be triggered gas (natural gas or propane), or electrically powered using a combination of heat pump and conventional electric heating element.
Operation
Gas hybrid water heaters use a modular infrared burner that is triggered by a water flow or thermostat. A multi-pass heat exchanger pushes the heat down and then recycles it through a shocked pipe for maximum efficiency. Water fills the reservoir from the bottom up and spreads evenly across the heating pipe, producing continuous hot water with consistent pressure and temperature.
During low flow situations, hybrids behave like tank type heater with minimum fuel usage and thermostat activation. Although equipped with some storage capacity, small volume minimizes the use of standby fuel. Hybrids also share additional properties with tank type heaters such as floor mounting, standard PVC ventilation, draining pots, and they can be fitted with recirculation pumps for greater water efficiency.
During high demand, high flow situations, hybrid technology behaves more like a tankless heater, with high BTU capacity and full modulation to supply continuous hot water flow across multiple applications. This produces fuel efficiency similar to a tankless heater, but with a higher flow capacity.
Efficiency
Heater control without tanks
Tankless water heaters can be subdivided into two categories according to their heating capability: "full to/full" versus "modulated". The full on/full off unit does not have a variable power output level; unit completely or completely dead. This may cause disturbing temperature variations of hot water and may be dangerous because the flow of water through the heater varies. The modulated tankless water heater changes its heat output in response to the flow rate of water flowing through the unit. This is usually done using flow sensors, modulated gas valves, inlet water temperature sensors, and water-outlet-choke temperature sensors. The properly regulated modulated heater can supply the same water-output temperature at different water flow rates in its rated capacity, usually maintaining a close range Ã, Â ± 2 Ã, Â ° C.
A combination of high-efficiency condensing boilers provides both space heating and water heating, and is an increasingly popular choice in UK homes. In fact, the combination boiler now accounts for more than half of all new domestic boilers installed in the UK.
Under current North American conditions, the most cost-effective configuration from a frequent operating point of view is to install a central (tank-type or no tank) central water heater for most homes, and to install a water heater without a POU tank on a remote faucet or room bath. However, the most economical design can vary according to the relative price of electricity, gas and water at the site, the layout of the building, and how much (and when) hot water is used. Only water heater without electric tank is widely available for many years. and they are still used for low-cost POU heating, but natural gas and propane POU heaters are now available for consideration.
Non-tank advantage
Source of the article : Wikipedia
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