District heating load profiles for domestic hot water preparation with realistic simultaneity using DHWcalc and TRNSYS

Braas, Hagen; Jordan, Ulrike; Best, Isabelle; Orozaliev, Janybek; Vajen, Klaus

doi:10.1016/j.energy.2020.117552

Cited by 47 publications

(14 citation statements)

References 6 publications

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“…There is a trade-off between the rate of false peaks and potential faults, which fall within the acceptable limits. The lines show almost the same regressions through the DHW preparation systems of the same building types [6]. However, the modelled temperature in the older building varies more significantly than in the new ones.…”

Section: Resultsmentioning

confidence: 61%

“…3 and 4 show, that for similar relations between circulation and DHW flow rates, the systems with a single HE result in higher circulating flows than the substations with no one. Braas et al [6] achieve the same conclusion, but the difference is related to pre-heater and after-heater configuration compared to a single heat exchanger. However, to make a valid comparison, the same buildings have to be simulated with both systems [6], as we do below.…”

Section: Resultsmentioning

confidence: 74%

“…Braas et al [6] indicate the correlation of the return temperature with circulation losses and useful energy demand for DHW, especially for instantaneous systems. The Kristensen et al's [7] database is stipulated by using two data fields to obtain only the single-family houses in Aarhus, Denmark municipality, so there is no particular focus on DHW consumption of residential multi-storey buildings.…”

Section: Introductionmentioning

confidence: 99%

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Specifying DHW heat demand profiles according to operational data: enhancing quality of a DH system model

et al. 2021

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For a DH network a meticulous analysis is required to detect a correlation of a reduction in energy demand from one year to another. The factors, which lead to such inconsistency, force an energy company (1) to modernize equipment at a consumer side and (2) to lower network operating temperatures. It results into so called fourth generation district heating (4GDH). The current research focuses on large-scale DH systems and DHW as second largest share of heat demand. The heat delays, thermal inertia and DHW consumption patterns are specified further since they might represent a natural heating accumulator. In this case, daily flow changes are considered, as they influence a DH system performance and desirable TES capacity. However, more precise profiles can be achieved by detecting the actual flow curve, and measuring the temperature difference between substation supply and return line. The dimensioning of DH systems requires comprehensive understanding of simultaneity factors. Thus, we consider substations with DHW preparation to choose the optimal size of the heat distribution network according to the new method. Case study is a DH system in Omsk, which includes residential houses (both SH and DHW coverage), and university buildings (more demand results from process heat). The operation of the system was studied for the period from the 1st of January to 31st of December 2020. We suggest a TES with a capacity of 0.04 MWh; based on the traditional temperature range, the volume is about 0.5 m3. Daily compensation time is 2-3 hours, when there is a reduction in the supply flow rate of 1500 t/h with minimum DH plant make-up. The entire DH system requires about 400 t of hot water make-up to reach the quasi-steady state conditions after the night DHW shutdown. Using the threshold of the traditional model, it hardly fits an operational value - it is better set according to novel method (0.1 MW). For similar relations between circulation and DHW flow rates, the systems with a HE result in higher circulating flows than the substations with no one. The consumer benefit from consuming DHW and heat according to more accurate profiles accounts 1.72 billion USD. It is quantified by considering avoiding using a back-up electricity source to ensure DHW service when a DH plant supplies enough heat. Moreover, if a TES is controlled according to the method detailed, it alleviates the stress for intermittent operation by compensating the transients of SH and DHW loads. 4GDH concept should be considered according to: (1) the operational data, (2) new DHW demand assessments, and (3) using TES to buffer peaks.

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Section: Resultsmentioning

confidence: 61%

Section: Resultsmentioning

confidence: 74%

Section: Introductionmentioning

confidence: 99%

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Specifying DHW heat demand profiles according to operational data: enhancing quality of a DH system model

et al. 2021

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“…Then, the duration curve was defined by adding the profiles for each type of building connected to the DHC network. Even if the local DHW usage presents typical patterns with peaks in the morning and the evening according to the different building destinations [51,52], the total daily DHW energy consumption for the entire urban area gets fairly constant throughout the year [4]. Small differences typically occur during summer in relation to holiday periods.…”

Section: Network Annual Energy Consumptionmentioning

confidence: 99%

Double Loop Network for Combined Heating and Cooling in Low Heat Density Areas

et al. 2020

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This study investigated a double loop network operated with ultra-low supply/return temperatures of 45/25 °C as a novel solution for low heat-density areas in Denmark and compared the proposed concept with a typical tree network and with individual heat pumps to each end-users rather than district networks. It is a pump-driven system, where the separate circulation of supply and return flow increased the flexibility of the system to integrate and displace heating and cooling energy along the network. Despite the increased use of central and local water pumps to operate and control the system, the simulated overall pump energy consumption was 0.9% of the total energy consumption. This was also an advantage at the design stage as the larger pressure gradient, up to 570 Pa/m, allowed minimal pipe diameters. In addition, the authors proposed the installation of electrically heated vacuum-insulated micro tanks of 10 L on the primary side of each building substation as a supplementary heating solution to meet the comfort and hygiene requirements for domestic hot water (DHW). This, combined with supply water circulation in the loop network, served as a technical solution to remove the need for bypass valves during summer periods with no load in the network. The proposed double loop system reduced distribution heat losses from 19% to 12% of the total energy consumption and decreased average return temperatures from 33 °C to 23 °C compared to the tree network. While excess heat recovery can be limited due to hydraulic issues in tree networks, the study investigated the double loop concept for scenarios with heat source temperatures of 30 °C and 45 °C. The double loop network was cost-competitive when considering the required capital and operating costs. Furthermore, district networks outperformed individual heat pump solutions for low-heat density areas when waste heat was available locally. Finally, although few in Denmark envisage residential cooling as a priority, this study investigated the potential of embedding heating and cooling in the same infrastructure. It found that the return line could deliver cold water to the end-users and that the maximum cooling power was 1.4 kW to each end-user, which corresponded to 47% of the total peak heat demand used to dimension the double loop network.

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“…In a recent study, Braas et al (2020) developed a method for generating heat profiles for domestic water heaters to find the most cost-efficient heating solution. They note the importance of draw-off profiles and appropriate time intervals.…”

Section: Introductionmentioning

confidence: 99%

Optimal schedule and temperature control of stratified water heaters

Engelbrecht

Ritchie

Booysen

2021

Energy for Sustainable Development

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Water heating is a major component of domestic electrical energy usage, in some countries contributing to 25 % of the residential sector energy consumption. Demand response strategies can reduce the time-of-use costs and overall electrical energy consumption. We present a method to reduce the electrical energy usage itself. Our novel heating schedule control minimises the electric water heater's energy usage without compromising user convenience. We achieve optimal control, while taking into account the natural temperature stratification of the water in the tank, using the A* search algorithm. Since previous research assumes a one-node thermal model, we also assess the effect of excluding stratification. We match three optimal control strategies to a baseline: the standard "always on" thermostat control. The first two strategies respectively match the temperature and the energy of the hot water supplied by the water heater. The third, a variation on the second, includes a method of preventing the growth of Legionella bacteria. We tested 77 water heaters over four weeks, a week for each season, and all three strategies saved energy. The median savings were 6.3 % for temperature-matching, 21.9 % for energy-matching and 16.2 % for energy-matching with Legionella prevention. Taking stratification into account increased these savings by 1.2 %, 5.4 % and 5.5 % respectively.

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District heating load profiles for domestic hot water preparation with realistic simultaneity using DHWcalc and TRNSYS

Cited by 47 publications

References 6 publications

Specifying DHW heat demand profiles according to operational data: enhancing quality of a DH system model

Specifying DHW heat demand profiles according to operational data: enhancing quality of a DH system model

Double Loop Network for Combined Heating and Cooling in Low Heat Density Areas

Optimal schedule and temperature control of stratified water heaters

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