Heat Loss Due to Domestic Hot Water Pipes

Abstract

Domestic hot water (DHW) system energy losses are an important part of energy consumption in newly built or in reconstructed apartment buildings. To reach nZEB or low energy building targets (renovation cases) we should take these losses into account during the design phase. These losses depend on room and water temperature, insulation and length of pipes and water circulation strategy. The target of our study is to develop a method which can be used in the early stages of design in primary energy calculations. We are also interested in how much of these losses cannot be utilised as internal heat gain and how much heat loss depends on the level of energy performance of the building. We used detailed DHW system heat loss measurements and simulations from an nZEB apartment building and annual heat loss data from a total of 22 apartment buildings. Our study showed that EN 15316-3 standard equations for pipe length give more than a twice the pipe length in basements. We recommend that for pipe length calculation in basements, a calculation based on the building’s gross area should be used and for pipe length in vertical shafts, a building’s heating area-based calculation should be used. Our study also showed that up to 33% of pipe heat losses can be utilised as internal heat gain in energy renovated apartment buildings but in unheated basements this figure drops to 30% and in shafts rises to 40% for an average loss (thermal pipe insulation thickness 40 mm) of 10.8 W/m and 5.1 W/m. Unutilised delivered energy loss from DHW systems in smaller apartment buildings can be up to 12.1 kWh/(m2·a) and in bigger apartment buildings not less than 5.5 kWh/(m2·a) (40 mm thermal pipe insulation).

A Facility’s Energy Demand Analysis for Different Building Functions

“…The calculated degree-day values from the daily minimum and maximum temperatures measured from 1991 to 2020 are shown in Figure 8 (Δti = 0 °C). The values of the constants a−f appearing need to be determined using Equation (7). The values in Table 2 were optimized for the Debrecen data (1991-2020; all three building functions; Δti = ±3 °C) using the built-in Solver subroutine "GRG Nonlinear" in Microsoft Excel.…”

“…In the cooling season, higher deviations can occur, up to a difference of 9.4%. This value can be misleading, as the cooling degree-day value is much The values of the constants a−f appearing need to be determined using Equation (7). The values in Table 2 were optimized for the Debrecen data (1991-2020; all three building functions; ∆t i = ±3 • C) using the built-in Solver subroutine "GRG Nonlinear" in Microsoft Excel.…”

“…The ratios can vary between countries due to differences in applicable comfort categories [3] and variable radiative heat gains [4]. Energy requirements can be reduced through various methods, such as the insulation of buildings [5,6] and mechanical systems [7,8] or through thoughtful operational strategies [9]. Previous research has shown that regulatory policies are the most effective means of reducing energy consumption in residential heating, highlighting the need for increased attention to this area for successful energy reduction [10].…”

A Novel Dynamic Approach to Cost-Optimal Energy Performance Calculations of a Solar Hot Water System in an nZEB Multi-Apartment Building

“…The reviewed studies usually deal with individual modules [22][23][24][25], but there were no studies found in which the overall calculation was performed with the goal of finding a cost-optimal solution. Hence, the main novelty of this study is in demonstrating the applicability and reliability of the overall complex and comprehensive calculation procedure, based on the new EPB standards for assessing the energy performance of a building.…”

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

“…Building codes in Wisconsin mandate the use of a recirculating system or electrical heating tape where the source to appliance distance exceeds 30 m [12]. Hamburg [18] measured heat losses from DHW circulation pipes in multi-occupant apartment blocks and correlated their data against pipe length and floor area.…”