Overview of Solutions for the Low-Temperature Operation of Domestic Hot-Water Systems with a Circulation Loop

Abstract

The operation of typical domestic hot water (DHW) systems with a storage tank and circulation loop, according to the regulations for hygiene and comfort, results in a significant heat demand at high operating temperatures that leads to high return temperatures to the district heating system. This article presents the potential for the low-temperature operation of new DHW solutions based on energy balance calculations and some tests in real buildings. The main results are three recommended solutions depending on combinations of the following three criteria: district heating supply temperature, relative circulation heat loss due to the use of hot water, and the existence of a low-temperature space heating system. The first solution, based on a heating power limitation in DHW tanks, with a safety functionality, may secure the required DHW temperature at all times, resulting in the limited heating power of the tank, extended reheating periods, and a DH return temperature of below 30 °C. The second solution, based on the redirection of the return flow from the DHW system to the low-temperature space heating system, can cool the return temperature to the level of the space heating system return temperature below 35 °C. The third solution, based on the use of a micro-booster heat pump system, can deliver circulation heat loss and result in a low return temperature below 35 °C. These solutions can help in the transition to low-temperature district heating.

Optimisation of a recirculating domestic hot water system to minimise wait time and heat loss

“…6 shows the propagation velocity along iso-temperature lines. This velocity drops below the flow velocity at the end of the initial step region and is thereafter close to the interface velocity from [2].…”

“…They identified on-demand heaters as a way of reducing pipework heat losses, giving energy savings of 550 kWh per annum if replacing a high temperature tank and quantified the energy use for a variety of installation options. Similarly Benakopoulos [2] describes recirculation systems for apartment blocks in Denmark and Poland with circulation heat losses of up to 70%. A well-insulated system is therefore essential.…”

“…Fig.6. Method of Lines solution comparing the interface velocity (lines across the surface) with the flow and interface velocities from equation[2] forTw ¼ T0 þ f T inlet À T0 ð Þ , f ¼ 1 À e À0:5 ; 0:5; 1 À e À1 È É. (Conditions as Fig.5).…”

Grouped Charging of Decentralised Storage to Efficiently Control Collective Heating Systems: Limitations and Opportunities

“…The operation of collective heating networks is also optimised when both SH and DHW demand are included. Benakopoulos et al [27] presented a general overview of possible concepts for DHW production with low-temperature DH. Their focus was on the recirculation loop of 4-pipe systems in an apartment building (connected to a DH) rather than controlling the supply temperature of the centralised network (i.e., the DH).…”

Heat Pump Systems in Existing Multifamily Buildings: A Meta‐Analysis of Field Measurement Data Focusing on the Relationship of Temperature and Performance of Heat Pump Systems

“…[ 13 ] New technologies such as ultrafiltration might enable temperature reduction without compromising water hygiene. [ 11,14 ]…”