A Key Review of Non-Industrial Greywater Heat Harnessing

Abstract

Abstract:The ever-growing concerns about making buildings more energy efficient and increasing the share of renewable energy used in them, has led to the development of ultra-low carbon buildings or passive houses. However, a huge potential still exists to lower the hot water energy demand, especially by harnessing heat from waste water exiting these buildings. Reusing this heat makes buildings more energy-efficient and this source is considered as a third-generation renewable energy technology, both factors conforming to energy policies throughout the world. Based on several theoretical and experimental studies, the potential to harness non-industrial waste water is quite high.As an estimate about 3.5 kWh of energy, per person per day could be harnessed and used directly, in many applications. A promising example of such an application, are low temperature fourth generation District Heating grids, with decentralized sources of heat. At the moment, heat exchangers and heat pumps are the only viable options to harness non-industrial waste heat. Both are used at different scales and levels of the waste-water treatment hierarchical pyramid. Apart from several unfavourable characteristics of these technologies, the associated exergetic efficiencies are low, in the range of 20-50%, even when cascaded combinations of both are used. To tackle these shortcomings, several promising trends and technologies are in the pipeline, to scavenge this small-scale source of heat to a large-scale benefit.

Opportunities and Threats of Implementing Drain Water Heat Recovery Units in Poland

“…However, the significance of waste heat is marginalized, which means that most of it is unproductively discharged to the environment and lost for good.A source of waste-to-energy that can successfully be used in buildings is wastewater [20,21]. The current development of technology allows recovery of heat deposited in wastewater both during transport and disposal, as well as directly at source [22,23]. Grey water discharged from sanitary facilities has a relatively high temperature, which in the case of showering oscillates at 35-40 • C. This allows the recovery of the heat deposited in them both by means of Drain Water Heat Recovery (DWHR) units [24] and using the heat pump [25].…”

Implementation of greywater heat recovery system in hospitals

“…The DWHR systems with HEX are widely used in residential, commercial and industrial buildings [10,12]. Particularly noteworthy is the heat recovery from greywater, which is characterized by significant high temperature, so it can be used to DHW preheating in buildings.…”

“…These values are dependent on the heat exchanger design. For the application of DWHR system, it is important that the HEX are double walled to avoid any leakages to the incoming clean drink water [12]. For this reason, it is not recommended using typical for systems of DHW preparation, JAD type shell and tube heat exchangers.…”

Numerical analysis and simulation of the heat recovery from wastewater using heat exchanger

“…One of the secondary energetic resources that on which a greater accent has been put worldwide are wastewaters (liquid waste). Wastewater from all sources except toilets, enters the sewage system at a relatively high temperature and with an exergy content [1,2]. Clearly, the heat content of wastewater is a major loss source, so it must be addressed as a solution to reduce energy consumption in both residential and commercial buildings [3].…”

“…The potential for domestic wastewater recovery is quite high, approximately 3.5 kWh of energy / person / day, which could be capitalized and used directly in several areas. [2] The recovery of secondary energetic resources and of liquid waste with high energetic content also led to the development and implementation of various types of heat exchangers and heat recuperators [4,5]. Heat exchangers are widely used in the industry, transportation, constructions, thermal power plants, heating and air conditioning systems, electronic equipment.…”