SISTEMAS ESTRUCTURANTES
DE LAS VÍAS Y EL TRANSPORTE
HOT WATER OF IEA DHC PARTICIPATING COUNTRIES
One of the main issues and challenges of low temperature district heating supply regarding hygienic aspects of domestic hot water DHW supply are temperature levels below 60 °C and sizes of the system of more than 3 litres (Brand 2013, Yang 2016 and Bartram et al. 2007). The required temperature levels for safe and hygienically unexceptionable DHW sup- ply vary from to country. Against this background an analysis of regulations and guidelines of the member countries participating in the project "IEA DHC Annex TS1" in the program “District Heating and Cooling” (DHC) of the International Energy Agency are analyzed and documented. An overview of the regulations and guidelines is given below.
Member
Country Description Standardisation
Denmark The national regulation DS 439 (DS 439 2009) states that the DHW system should be designed to be capable of preparing DHW at 60 °C and maintain at least 50 °C in all the distribu- tion lines. During peak load a minimum temperature level of 45 °C is sufficient. In contrast to EN 806 (EN 806-1:2000 and EN 806-2:2005) there is no differentiation in small and large systems. In traditional DHW systems, mostly due to large sys- tem volume of e.g. storages, it has to be ensured that the re- turn temperature from the DHW recirculation is 50 °C in order to prevent the risk of Legionella. As a consequence, the current DH minimum supply temperature is above 60 °C.
DS439:2009 Code of practi- ce for domestic hot water supply installation
Finland The temperature level in the entire DHW system has to be at least at 55 ° C. In case of peak load, this temperature may drop for maximal ten seconds. Due to the risk of scalding the maxi- mum permitted temperature level of DHW is 65 °C. In case of DH supply it is recommended that substations have to be de- signed so that the DHW from the heat exchangers (HE) is hig- her than 58 °C. In case of DHW commonly instantaneous HEs are used. As a result the current DH minimum supply tempe- rature is above 60 °C.
National Building Code of Finland D1: Water supply and sewerage equipment of properties, regulations and guidelines
(YM 2007)
Germany The regulation is valid for all new systems with a storage size > 400 litres and a hydraulic loops > 3 litres, if they are not installed in a single- or two-family houses. There should be at least 60 °C at the water outlet of the boiler. The temperature difference inside the pipe network is supposed to amount 5 °C maximum, circulation included. Pipes over several floors with a water volume > 3 litres should be equipped with an additi- onal circulation pipe or self-regulating trace heating. The cir- culation or electrical trace heating must not be interrupted for longer than 8 hours per day.
In case of DHW preparation using DH a hot water temperature of more than 60 °C has to be maintained in order to avoid con- tamination of the hot water system with legionella.
DVGW-Arbeitsblatt W551 - Technische Maßnahmen zur Minderung des Legionellen- wachstums in Neuanlagen (DVGW W551 2004)
Member
Country Description Standardisation
Great Britain The temperature level of the DHW systems including the sto- rage may not drop below 60 °C. At the tapping point a tempe- rature level 50 °C of DHW should be reached within one mi- nute, in buildings with high hygienic standards at 55 °C. Si- gnificant higher temperatures should be avoided because of the risk of scalding. In case of a DHW supply using instanta- neous heat exchangers, the required temperatures and time specifications do not have to be fulfilled. In case of using in- stantaneous heat exchangers it has to be ensured, that ins- tallation is directly connected to the DHW supply. The volume between pipe and heat exchanger should be less than one lit- re and the volume between heat exchanger and tapping point should less than 1.5 litres.
The maximum permissible temperature level of DCW is 20 °C.
HSG274 Legionnaires’ di- sease: Technical guidance Part 2 (HSE 2014)
Korea The required temperatures varies depending on the case of application:
Inlet temperature (heat generator) Central heating 120-180 °C (ΔT: 40 K)
District/local heating supply Seoul Housing & Communities Corporation: 115-60 °C (ΔT: 55 K)
Korea District heating Corporation: SH 115-50 °C (ΔT: 65 K) Required temperature level of the DHW inside the storage Central heating 60-50 °C (ΔT: 10 K)
Local heating 60-50 °C (ΔT: 10 K) District/local heating supply
Seoul Housing & Communities Corporation: 60-45 °C (ΔT: 15 K) Korea District heating Corporation: SH 60-45 °C (ΔT: 15 K)
Technical Guidelines (Se- oul Housing & Communities Corporation) (ISH 2017)
Norway The DHW system must be designed so that the temperature at any tap point in the system reaches at least 60 °C within one minute after opening a tap. The return temperature in DHW sys- tems with continuous water circulation must not be less than 60 °C. Due to hygienic reasons the whole DHW system must be flushed regularly with water at a temperature of at least 70 °C. The temperature in DHW storages must be at least 70 °C. The same conditions must be fulfilled for DHW connected to district heating systems.
Prevention of Legionel- la – guidelines, 3. edition, chapter 7. National Institu- te of Public Health (Petter- sen 2015)
Sweden Installations for domestic hot water should be designed so that a water temperature of less than 50 °C can be achieved af- ter the tap. To reduce the risk of scalding, the temperature of the hot tap water is limited to 60 °C after the tap. If there is a special risk of accidents the temperature of the hot tap water has to lower than 38 °C. Devices for control of DHW should be designed so that the risk of injury from the confusion of do- mestic hot and cold tap water is limited. The heat-up of the DCW system must be avoided.
6: BFS 2015:3 BBR 22 - Section 621 (BFS 2011:6)
Next to the detailed analysis of the regulations and guidelines of the IEA DHC Annex TS1 member countries, the regulations of further DHC member countries are reviewed. In Cana- da, electrical heat generators have a factory default settings of 60 °C. In the US the require- ment of warm water is at about 5,000 kWh per apartment and year which is nearly twice as the demand in Germany. This is mainly due to the reason that dishwasher and other sec- tors in industry and households are directly supplied with warm water. The operating tem- perature of condensing boilers is at 48 °C which is also suggested by the government (Dal- la Rosa et al. 2014). The general recommendation of the “ASHRAE Guideline 12-2000” (ASHRAE 2000) also used in Canada and the USA is a system temperature of 55 °C. In the Netherlands, the “Modelbeheersplan legionellapreventie in Leidingwater” obliges that the temperature of drinking warm water systems must not drop below 60 °C (VROM 2000). In
France, the temperature at the tapping point for personal hygiene should not exceed 50 °C, as it is regulated in “Arrête du 30 novembre 2005 modifiant l’arrêté du 23 juin 1978 - Ins- tallations for the distribution of domestic hot Water“ (JORF 2005). At other tapping points, temperatures up to 60 °C are allowed. In addition to that, it is distinguished in small and large plants analogically to the German regulation. For large-scaled plants, there are further specifications: the temperature at the generator outlet must not drop below 55 °C and the- re has to be a periodical thermal flush. In the Switzerland the national norm SIA 385 (SIA 385 2011) states that the outlet temperature of the water heaters should be 60 °C, the tem- perature level of warm kept pipes (circulation and warm keeping system till access into the water heater) is 55 °C and at the tapping point at least 50 °C. Systems with temperatures lower than 60 °C, e.g. fresh water stations, are possible, but they have to be heated up to 60 °C for one hour once a day (disinfection) (SIA 385 2011).
The analysis of the different regulations shows that regulations of the different countries are dealing mostly with traditional DWI with mostly high volumes for drinking water supply. The technical methods for the supply of drinking water, described as part of the regulations and guidelines, consider especially hygienic aspects due to a minimisation of health risks. Al- ternative and energy efficient methods are not or only insufficiently regarded.