Water heat recycling (also known as drain water heat recovery, waste water heat recovery, greywater heat recovery,[ citation needed ] or sometimes shower water heat recovery[ citation needed ]) is the use of a heat exchanger to recover energy and reuse heat from drain water from various activities such as dishwashing, clothes washing and especially showers. The technology is used to reduce primary energy consumption for water heating.
The cold water that is put into a water heating device can be preheated using the reclaimed thermal energy from a shower so that the input water does not need as much energy to be heated before being used in a shower, dishwasher, or sink. The water entering a storage tank is usually close to 11 °C but by recovering the energy in the hot water from a bath or dishwasher, the temperature of the water entering the holding tank can be elevated to 25 °C, saving energy required to increase the temperature of a given amount of water by 14 °C. This water is then heated up a little further to 37 °C before leaving the tank and going to the average shower. [1]
When recycling water from a bath (100–150 litres) or shower (50–80 litres) the waste water temperature is circa 20–25 °C. An in-house greywater recycling tank holds 150–175 litres allowing for the majority of waste water to be stored. Utilizing a built in copper heat exchange with circulation pump the residual heat is recovered and transferred to the cold feed of a combi-boiler or hot-water cylinder, reducing the energy used by the existing central heating system to heat water.[ citation needed ]
Heating water accounts for 18% of the average household utility bill. Standard units save up to 60% of the heat energy that is otherwise lost down the drain when using the shower.[ citation needed ]
Installing a water heat recycler reduces energy consumption and thus greenhouse gas emissions and the overall energy dependency of the household.
Typical retail price for a domestic drain water heat recovery unit ranges from around $400 to $1,000 Canadian. For a regular household, water heating is usually about 20% of overall energy demand. [2] The energy savings can result in an average payback time for the initial investment of 2–10 years.[ citation needed ]
A 2-year independent study of waste water heat recovery systems installed into residential houses in the UK found savings of 380kWh and 500kWh per person per year. [3]
A heat pump can be combined with municipal sewage lines to allow a large building's HVAC system recycle the winter heat or summer cool (compared to the outside air) of water flowing out of many homes and businesses. [4]
The reverse is also possible: heat from air conditioning and industrial chillers can be used to pre-heat water. [5] Heat rejected by a chiller system for providing air-conditioning to larger buildings can be recovered by installing a heat-exchanger between the incoming domestic cold water, and condenser water return. A conventional chilled water system rejects heat gathered by the condenser water loop from the refrigerant to a cooling tower. By diverting a fraction of mass flow rate of condenser water away from the cooling tower, and circulating it through a heat-exchanger (usually a plate-and-frame configuration), incoming domestic cold water can be pre-heated before reaching the boiler. This reduces the required increase in temperature of the water before it can be supplied to the end user, and therefore lowering boiler fuel burn.
An autonomous building is a building designed to be operated independently from infrastructural support services such as the electric power grid, gas grid, municipal water systems, sewage treatment systems, storm drains, communication services, and in some cases, public roads.
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR.
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment. The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air. Another example is the heat sink, which is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant.
A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons or to eliminate musty odor and to prevent the growth of mildew by extracting water from the air. It can be used for household, commercial, or industrial applications. Large dehumidifiers are used in commercial buildings such as indoor ice rinks and swimming pools, as well as manufacturing plants or storage warehouses. Typical air conditioning systems combine dehumidification with cooling, by operating cooling coils below the dewpoint and draining away the water that condenses.
Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.
A cooling tower is a device that rejects waste heat to the atmosphere through the cooling of a coolant stream, usually a water stream, to a lower temperature. Cooling towers may either use the evaporation of water to remove heat and cool the working fluid to near the wet-bulb air temperature or, in the case of dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature using radiators.
Cogeneration or combined heat and power (CHP) is the use of a heat engine or power station to generate electricity and useful heat at the same time.
Heat recovery ventilation (HRV), also known as mechanical ventilation heat recovery (MVHR) is a ventilation system that recovers energy by operating between two air sources at different temperatures. It is used to reduce the heating and cooling demands of buildings.
A thermal power station, also known as a thermal power plant, is a type of power station in which the heat energy generated from various fuel sources is converted to electrical energy. The heat from the source is converted into mechanical energy using a thermodynamic power cycle. The most common cycle involves a working fluid heated and boiled under high pressure in a pressure vessel to produce high-pressure steam. This high pressure-steam is then directed to a turbine, where it rotates the turbine's blades. The rotating turbine is mechanically connected to an electric generator which converts rotary motion into electricity. Fuels such as natural gas or oil can also be burnt directly in gas turbines, skipping the steam generation step. These plants can be of the open cycle or the more efficient combined cycle type.
A condensing steam locomotive is a type of locomotive designed to recover exhaust steam, either in order to improve range between taking on boiler water, or to reduce emission of steam inside enclosed spaces. The apparatus takes the exhaust steam that would normally be used to produce a draft for the firebox, and routes it through a heat exchanger, into the boiler water tanks. Installations vary depending on the purpose, design and the type of locomotive to which it is fitted. It differs from the usual closed cycle condensing steam engine, in that the function of the condenser is primarily either to recover water, or to avoid excessive emissions to the atmosphere, rather than maintaining a vacuum to improve both efficiency and power.
Renewable heat is an application of renewable energy referring to the generation of heat from renewable sources; for example, feeding radiators with water warmed by focused solar radiation rather than by a fossil fuel boiler. Renewable heat technologies include renewable biofuels, solar heating, geothermal heating, heat pumps and heat exchangers. Insulation is almost always an important factor in how renewable heating is implemented.
Energy recovery includes any technique or method of minimizing the input of energy to an overall system by the exchange of energy from one sub-system of the overall system with another. The energy can be in any form in either subsystem, but most energy recovery systems exchange thermal energy in either sensible or latent form.
An absorption heat pump (AHP) is a heat pump driven by thermal energy such as combustion of natural gas, steam solar-heated water, air or geothermal-heated water differently from compression heat pumps that are driven by mechanical energy. AHPs are more complex and require larger units compared to compression heat pumps. In particular, the lower electricity demand of such heat pumps is related to the liquid pumping only. Their applications are restricted to those cases when electricity is extremely expensive or a large amount of unutilized heat at suitable temperatures is available and when the cooling or heating output has a greater value than heat input consumed. Absorption refrigerators also work on the same principle, but are not reversible and cannot serve as a heat source.
A fan coil unit (FCU), also known as a Vertical Fan Coil Unit (VFCU), is a device consisting of a heat exchanger (coil) and a fan. FCUs are commonly used in HVAC systems of residential, commercial, and industrial buildings that use ducted split air conditioning or central plant cooling. FCUs are typically connected to ductwork and a thermostat to regulate the temperature of one or more spaces and to assist the main air handling unit for each space if used with chillers. The thermostat controls the fan speed and/or the flow of water or refrigerant to the heat exchanger using a control valve.
Energy recycling is the energy recovery process of using energy that would normally be wasted, usually by converting it into electricity or thermal energy. Undertaken at manufacturing facilities, power plants, and large institutions such as hospitals and universities, it significantly increases efficiency, thereby reducing energy costs and greenhouse gas pollution simultaneously. The process is noted for its potential to mitigate global warming profitably. This work is usually done in the form of combined heat and power or waste heat recovery.
An instant hot water dispenser or boiling water tap is an appliance that dispenses water at about 94 °C (201 °F) (near-boiling). There are hot-only and hot and cool water models, and the water may be filtered as well as heated. Instant hot water dispensers became popular in the 1970s. Instant hot water dispensers are very similar to portable shower devices; the latter is fitted with a heating element and quickly heats up water, once a switch has been activated.
A waste heat recovery unit (WHRU) is an energy recovery heat exchanger that transfers heat from process outputs at high temperature to another part of the process for some purpose, usually increased efficiency. The WHRU is a tool involved in cogeneration. Waste heat may be extracted from sources such as hot flue gases from a diesel generator, steam from cooling towers, or even waste water from cooling processes such as in steel cooling.
HVAC is a major sub discipline of mechanical engineering. The goal of HVAC design is to balance indoor environmental comfort with other factors such as installation cost, ease of maintenance, and energy efficiency. The discipline of HVAC includes a large number of specialized terms and acronyms, many of which are summarized in this glossary.
Tankless water heaters — also called instantaneous, continuous flow, inline, flash, on-demand, or instant-on water heaters — are water heaters that instantly heat water as it flows through the device, and do not retain any water internally except for what is in the heat exchanger coil unless the unit is equipped with an internal buffer tank. Copper heat exchangers are preferred in these units because of their high thermal conductivity and ease of fabrication. However, copper heat exchangers are more susceptible to scale buildup than stainless steel heat exchangers.
Cold district heating is a technical variant of a district heating network that operates at low transmission temperatures well below those of conventional district heating systems and can provide both space heating and cooling. Transmission temperatures in the range of approx. 10 to 25 °C are common, allowing different consumers to heat and cool simultaneously and independently of each other. Hot water is produced and the building heated by water heat pumps, which obtain their thermal energy from the heating network, while cooling can be provided either directly via the cold heat network or, if necessary, indirectly via chillers. Cold local heating is sometimes also referred to as an anergy network. The collective term for such systems in scientific terminology is 5th generation district heating and cooling. Due to the possibility of being operated entirely by renewable energies and at the same time contributing to balancing the fluctuating production of wind turbines and photovoltaic systems, cold local heating networks are considered a promising option for a sustainable, potentially greenhouse gas and emission-free heat supply.
