Delivery efficiency of the Jaga Low H 2 O heat exchanger in a Tempo enclosure

Transcription

1 Delivery efficiency of the Jaga Low H 2 O heat exchanger in a Tempo enclosure Determination of the delivery efficiency for a quality declaration for the ISSO database

2 Delivery efficiency of the Jaga Low H 2 O heat exchanger in a Tempo enclosure 2014 Kiwa N.V. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, whether electronic, mechanical, photocopying, recording, or in any other way, without the prior written permission of the publisher. Determination of the delivery efficiency for a quality declaration for the ISSO database Colophon Kiwa Technology B.V. Wilmersdorf 50 Postbus AC Apeldoorn Tel Fax Title Delivery efficiency of the Jaga Low H 2 O heat exchanger in a Tempo enclosure Project number Project manager ir. M.J. Kippers Client Jaga-Konvektco Nederland B.V. J. Verdonck Quality assurer(s) ir. J.C. de Laat Author(s) ing. E.F.J. Fennema, ir. M.J. Kippers This report is not public and is only provided to the clients of the contract research project/consulting project. Any further distribution will be by the client itself.

3 Summary Jaga-Konvektco has developed the Low H 2 O heat exchanger, which provides energy savings compared to a standard radiator. Jaga likes to use this energy saving as a selling point. Jaga intends to have the Low H 2 O heat exchanger included in the database that is linked to the energy performance standard (EPN) by means of a quality certificate. The energy savings of the Low H 2 O heat exchanger are therefore also included in the energy performance coefficient calculation. The database with quality declarations is managed by ISSO (knowledge institute for the installation sector.) Using simulations, which are based on national and international standards, and measurements performed by Jaga-Konvektco, Kiwa Technology has calculated the energy savings of the Low H 2 O heat exchanger. The energy savings of the Low H 2 O heat exchanger are at least 5%. The quality declaration for the Low H 2 O heat exchanger in a Tempo enclosure is set out in the annex

4 Contents Summary 1 1 Introduction Background Jaga Low H 2 O heat exchanger with Tempo type 15 enclosure Task: Calculation of the delivery efficiency of the Low H 2 O heat exchanger Report layout 5 2 The Low H 2 O heat exchanger is more energy efficient than standard radiators Result is at least 5% energy saving The delivery efficiency is determined using an annual simulation of the Low H 2 O heat exchanger in a standard home The simulation is modular Modelling of the Jaga Low H 2O 7 Literature list 9 I Calculation of the delivery efficiency 10 II Modelling of the Jaga Low H 2 O heat exchanger 11 III Quality declaration: delivery efficiency 'l H,em of Jaga Low H 2 O heat exchanger in a Tempo enclosure

5 1 Introduction 1.1 Background The energy performance of a building depends, among other things, on the efficiency of the delivery system. These delivery systems include the radiators. The energy performance is calculated on the basis of the "Energy performance standard for buildings" (EPG, NEN7120). NEN 7120 "Energy performance standard for buildings" (EPG) - based on the European Energy Performance Buildings Directive (EPBD) The efficiency of delivery systems using default values (standard route) all delivery systems have the same efficiency no possibility for evaluating innovative energy-efficient delivery systems default values included in NEN 7120 The efficiency of delivery system based on quality declaration (alternative route) distinguish between delivery systems in terms of efficiency recognition for innovative energy-efficient delivery systems quality declaration included in the ISSO "verified quality declaration database" quality declaration issued by Kiwa Energy performance of the building As standard the EPG assumes default values for the delivery efficiency of delivery systems under various conditions. However, the standard also offers the alternative to evaluate the delivery efficiency through a quality declaration. The quality declaration has the advantage that a distinction can be made between different delivery systems based on their efficiency. Innovative energy-efficient delivery systems can therefore make a positive contribution to the calculated energy performance of a building and in this way are competitive. ISSO (knowledge institute for the installation sector) assesses the validity of quality declarations and manages the "verified quality declaration database". 1.2 Jaga Low H 2O changer combined with Tempo type 15 enclosure The Jaga Low H 2 O Tempo is a heat emission system based on a heat exchanger in an enclosure as shown in figure 1, 2 and 3. Figure 1: Jaga Low H 2 O heat exchanger Figure 2: Jaga enclosure Tempo type

6 Figure 3: Jaga Low H 2 O heat exchanger in Tempo plus type 15 (wall mounted model) The Low H 2 O heat exchanger is made of copper tubes and corrugated aluminium fins. The serial matrix-flow channels (Figure 1) ensure a good heat transfer of central heating-water to the air. Due to the compact design, the Low H 2 O heat exchanger contains relatively little water and steel parts. Thus, the exchanger reacts fast to a heat demand and does not heat up unnecessarily when the optimum indoor temperature is reached. The heat exchanger is mounted at the bottom of the enclosure. Since the beginning of 2014, the Jaga Tempo type 15 conversion has an insulating layer on the wall side to limit the loss of energy to the outside. The Jaga exchanger differs from a conventional radiator in the way described below, which is relevant for the EN7120: Advantages: o The surface of the heat exchanger is significantly smaller than a conventional radiator. This leads to less radiation loss through the back wall. o The insulating layer in the enclosure on the wall side limits the energy losses to the back wall. o Significantly smaller heat capacity results in a faster response time for heat output during a 'cold start'. Disadvantages: o The lower temperature and smaller surface results in a smaller radiation component in the Fanger comfort equation. o The convection losses to the back wall are higher because there is a bigger air flow along the back wall. 1.3 Task: Calculation of the delivery efficiency of the Low H 2O heat exchanger Jaga-Konvektco has commissioned Kiwa Technology to calculate the delivery efficiency of the Low H 2 O heat exchanger mounted in a type 15 Tempo enclosure. Kiwa Technology has developed a simulation model for this exchanger. The simulation model is based on an existing model that was also used for an earlier quality declaration of a delivery system. Use is also made of the existing model of the reference radiator from the previous project. The simulations were then carried out for the purposes of the quality declaration. Furthermore, Kiwa Technology supervises the process for the ISSO request

7 1.4 Report layout In the following chapter the realisation of the calculated delivery efficiencies is presented as well as the annual simulation of the radiators in a standard house. The quality declaration is included within the annex

8 2 The Low H 2 O heat exchanger is more energy efficient than standard radiators The delivery efficiency of the Low H 2 O heat exchanger is higher than the delivery efficiency of standard radiators. This is the result of a year s simulation of both radiators in a standard home. The energy performance of a building is, to a large extent, determined by the required energy for space heating. The delivery efficiency together with the generation and distribution efficiency determines the overall efficiency of the heating system. The delivery efficiency has an influence in the determination of the EPC of a building. A more efficient radiator therefore gives a better EPC rating of the building. In this chapter the calculated delivery efficiencies are presented as well as the annual simulation of the radiators in a standard house. 2.1 Result is at least a 5% energy saving Table 1 shows the calculated delivery efficiency of the Low H 2 O heat exchanger {ri H,calc,LH2O ) and the calculated delivery efficiency of the standard radiator type 22 {ri H,calc,std ). The reference delivery efficiency of the standard radiator (ri H,ref,std ) from EN7120 [Lit 1] is also shown. The reference delivery efficiency for the Low H 2 O heat exchanger (ri H,ref,LH2O ) is the calculated delivery efficiency (ri H,calc,LH2O ) of the competitor product ECO radiator scaled with the relationship between the calculated delivery efficiency (ri H,calc,std ) and reference delivery efficiency (ri H,ref,LH2O ) of the standard radiator, see annex I: This is the efficiency that is included in the quality declaration. Simulations were carried out for low and high average delivery temperatures and for newbuild and existing buildings. The simulations are based on standard tests from the standard for energy performance of buildings [Lit 4]. Table 1: Delivery efficiency of the Low H 2 O standard heat exchanger calculated with the annual simulation Test Average delivery temperature: 50 C Average delivery temperature: >50 C STD radiator Low H 2 O STD radiator Low H 2 O ri H,calc,std [-] ri H,ref,std [-] ri H,calc,LH2O [-] 'l H,ref,LH2O [-] ri H,calc,std [-] ri H,ref,std [-] ri H,calc,LH2O [-] 'l H,ref,LH2O Newbuild Existing building The annual simulations show that the calculated delivery efficiency of the Low H 2 O heat exchanger is higher than the calculated delivery efficiency of standard radiators. The Low H 2 O heat exchanger achieves at least a 5% energy saving compared with a standard radiator. The delivery efficiency is averaged and is rounded down to 0.05 in accordance with EN7120 [Lit 1]. The delivery efficiency is summarised in the quality declarations in annex III, where a maximum value of 1.00 is used as agreed with ISSO. [-] - 6 -

9 2.2 The delivery efficiency is determined using an annual simulation of the Low H 2 O heat exchanger in a standard house Kiwa Technology has proven the energy saving of the Low H 2 O heat exchanger with the help of the software package Matlab/Simulink. A standard home was simulated [Lit 1] containing a standard parallel radiator or a Low H 2 O heat exchanger. In Chapter there is a description of the general simulation model. Then in chapter the Low H 2 O heat exchanger model is described which is contained within The simulation is modular The modular structure of the model is shown schematically in Figure 4. It consists of three levels. Simulation (verified according to EN15265 with standard radiator) Building subsystem Radiator subsystem LH2O or standard Internal heat Heat emission Ventilation Climate Sun Thermostat Figure 4: Structure of the simulation model to determine the performance of the Low H 2 O standard heat exchanger and standard radiator At the top level external conditions are configured, including internal heat, heat emission, ventilation, climate and sun, these are then presented to the subsystems 'building subsystem' and 'radiator subsystem'. The second level concerns the 'building subsystem'. This subsystem contains the model of a standard room and is based on EN7120 [Lit 1]. The third level contains a detailed simulation of a standard or a Low H 2 O heat exchanger. The theoretical model of the Low H 2 O heat exchanger is validated on the basis of a practical measurement by Jaga-Konvekto according to EN442, [Lit 6]. The complete model is validated according to EN15265 [Lit 4] by calculating a number of cases, in which a standard radiator is used Modelling of the Jaga Low H 2O The Jaga Low H 2O heat exchanger with the associated heat transfer mechanisms, is shown in figure 5. In the middle of the figure there is the heat exchanger, including enclosure and insulation, seen mounted on the wall. The heat exchanger radiates to the enclosure and the insulation on the wall. The warm air carries heat to the enclosure and the insulation on the wall by forced convection. The wall carries heat to the outside air by radiation and free convection. The enclosure also carries heat to the air in the room by radiation and free convection. The heat transfer at the wall and enclosure are magnified on the sides

10 Insulation Wall Enclosure Heat exchanger Figure 5: Jaga Low H 2 O heat exchanger with heat transfer mechanisms The elaboration of this model is shown in annex II

11 Literature list Lit 1 Lit 2 Lit 3 Lit 4 Lit 5 Lit 6 NEN 7120:2011, Energy performance of buildings Determination method NEN-EN :2007, Heating systems in buildings - method of calculating the energy requirement and the system efficiency - Part 2-1: Delivery systems for space heating NEN-EN-ISO 13790:2008, Energy performance of buildings - Calculation of energy use for space heating and cooling NEN-EN 15265:2007, Energy performance of buildings - Calculation of energy needs for space heating and cooling using dynamic methods - General criteria and validation procedures NEN-EN-ISO 6946:1997, Components and elements of buildings thermal resistance and thermal transmittance determination method (ISO 6946:1996) NEN-EN 442-2:1996, Radiators and convectors - test methods and presentation of the performance Lit 7 polytechnic notebook G1/9, 48 th Edition, Royal PBNA, 1998) - 9 -

12 I Calculation of the delivery efficiency The delivery efficiency is the ratio between the heat demand and the heat delivered to the house: Q H;nd rih Q H;em With rih the delivery efficiency [-] the heat demand [MJ] Q H;nd Q H;em the supplied heat [MJ] The calculated delivery efficiency (ri H,calc,LH2O ) of the Low H 2 O heat exchanger is scaled based on a reference delivery efficiency for the Low H 2 O heat exchanger {ri H,LH2O ) with the relationship between the calculated delivery efficiency (ri H,calc,std ) and reference delivery efficiency (ri H,ref,std ) of the standard radiator: H, LH 2O H,ref,std ri H,calc,LH 2O ri H,calc,std

13 II Modelling of the Jaga Low H 2 O heat exchanger The Jaga Low H 2 O heat exchanger with the associated heat transfer mechanisms, is shown in Figure 5. In Figure 6 the Jaga Low H 2 O heat exchanger is shown in a lumped capacitance scheme. Radiation (Q3) T exchanger Radiation (Q1) T wall inside Conduction (Q2) T wall outside T outside Convection (Q6) Convection (Q4) Radiation (Q5) Radiation (Q9) T air Convection (Q7) T enclosure inside Conduction (Q8) T enclosure outside T room Convection (Q10) Air which is flowing out on the top of the enclosure (Q11) T air out Figure 6: Lumped capacitance scheme of the Jaga Low H 2 O heat exchanger This scheme consists of five known parameters and 20 unknown parameters, see Table 2. The 20 unknown parameters are to be solved using the equations from Table 2 that in are worked out in Table 3. Known parameters Unknown parameters Comparison T exchanger T air T outside T room Q in T inside wall T outside wall T enclosure inside T enclosure outside T air out Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Heat transfer Q1 Heat transfer Q2 Heat transfer Q3 Heat transfer Q4 Heat transfer Q5 Heat transfer Q6 Heat transfer Q7 Heat transfer Q8 Heat transfer Q9 Heat transfer Q10 Law of conservation of energy (thermal pull) Law conservation of energy (system limits) Energy balance node A Energy balance node B Energy balance node C Energy balance node D

14 Q12 Q13 Q14 Q15 Energy balance node E Energy balance node F Energy balance node G Energy balance node H Table 2: Model parameters and equations Q1 Radiation from the exchanger to the enclosure The radiation is calculated by: Q =A F L f3 (T 4 -T 4 ) rad exch wall with A F L f3 T exch T wall = [m 2 ] surface (top of the exchanger) = [-] view factor = [-] emission factor = [W/(m 2 K 4 )] Boltzmann constant = [K] temperature of the exchanger = [K] temperature of the wall Q2 conduction through the wall The heat transfer is calculated using the equation for heat transfer by conduction. Q = k/l A T [W] heat transfer k = [W/(m K)] thermal conductivity coefficient l = [m] wall thickness A = [m 2 ] area of the wall above the exchanger within the enclosure T = T wall inside -T wall outside [K] Q3 Radiation from the outer wall to the outside See equations Q1 Q4 Convection from the outer wall to the outside The heat transfer is calculated using the equation for heat transfer by free convection along a vertical wall. Q = h A T [W] heat transfer h = N ux k/l [W/(m 2 K)] A = [m 2 ] surface of the wall T = T wall outside -T outside [K] N ux = 0.671*(Pr/(Pr Pr (1/2) )) Ra = (g f3)/(a v) l 3 T [-] Rayleigh number (g f3)/(a v) = air property (1/4) Ra (1/4) Q5 Radiation of the exchanger to the enclosure See equations Q1 Q6 Convection to the inner wall

15 The heat transfer is calculated using the equation for heat transfer by forced internal convection. Q = h A T [W] heat transfer h = Nu D k/d h [W/(m 2 K)] A = [m 2 ] area of the wall above the exchanger within the enclosure T = T air -T wall [K] k = [W/(m K)] thermal conductivity coefficient D h = 4 A/p [m] hydraulic diameter (A = surface; p = perimeter) (1/3) Nu D = (Nu (Nu 2-0.7) ) Nu 1 = 3.66 Nu 2 = (Re Dh Pr D h /l) (1/3) Re Dh = v i D h,i /v [-] Reynolds number v = [m 2 /s] kinematic viscosity of air Pr = 0,72 [-] Prandtl number Q7 Convection to the enclosure (inside) See equations Q6 Q8 Conduction by the enclosure See equations Q2 Q9 Radiation from the enclosure to the room See equations Q1 Q10 Convection from the enclosure to the room See equations Q4 Law conservation of energy (thermal pull (as part of convection)) The thermal pull (flow rate of air) is calculated using the law of conservation of energy and the law of conservation of mass. P = P 1 + P 2 + P 3 + P 4 + P 5 = ( g l [Pa]] (law of conservation of energy) p 5 P 1 = [Pa] pressure loss at entry of the exchanger 1 ( v 2 P 2 = ( 2 l/d h wis 0,5 v 2 2 [Pa] pressure loss between the lamella of the exchanger P 3 = ( 3 0,5 v 2 enclosure 3 [Pa] pressure loss at transition from the exchanger to the p 4 P 5 = ( 5 0,5 v 5 4 [Pa] pressure loss in the enclosure p 3 P 5 = ( 5 0,5 v 5 [Pa] pressure loss at exit of the enclosure p 2 v

16 = v 4 = v 3 = v 2 = v 1 m/s] (law of conservation of mass) p 1 with g = 9.81 [m/s 2 ] gravitational acceleration l = [m] height of the lamella = [kg/m 3 ] density of air v i = [m/s] air speed ( 1 = 1 [-] friction factor ( 2 = 4 24/Re Dh [-] friction factor

17 ( 3 = 1 [-] friction factor ( 4 = 4 24/Re Dh [-] friction factor ( 5 = 1 [-] friction factor D h = 4*A/p [m] hydraulic diameter (A = surface; p = perimeter) Re Dh = v i D h,i /v [-] Reynolds number v = [m 2 /s] kinematic viscosity of air The heat transfer is calculated using the equation for heat transfer by forced convection. Q = A T [W] heat transfer with = Pr 1/3 Re 1/2 [W/(m 2 K)] Nusselt number A = [m 2 ] projected surface of the exchanger on the wall Pr = 0,72 [-] Prandtl number Law conservation of energy (system limits) Qin=Q12+Q13=Q14+Q15+Q11 Energy balance node A Q12=Q1+Q5 Energy balance node B Q1+Q6=Q2 Energy balance node C Q2=Q3+Q4 Energy balance node D Q3+Q4=Q14 Energy balance node E Q13=Q6+Q7+Q11 Energy balance node F Q5+Q7=Q8 Energy balance node G Q8=Q9+Q10 Energy balance node H Q9+Q10=Q

18 III Quality declaration: delivery efficiency 'l H,em of Jaga Low H 2 O heat exchanger in a Tempo enclosure Individual heating or district heating with individual metering. Height in computation zone space of up to 8m. Heat delivery type of heating system 2a) Radiator heating and/or convector heating for outside wall d; average thermal resistance of the external partition elements e at the location of the radiators or convectors, Rc in m 2 K/W, equal to or larger than 2.5 2b) Radiator heating and/or convector heating for outside wall d; average thermal resistance of the external partition elements e at the location of the radiators or convectors, Rc in m 2 K/W, less than 2.5 Average delivery temperature 50ºC >50ºC

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