New Steps towards Compact Solar Combisystems in Scandinavia

New Steps towards Compact Solar Combisystems in Scandinavia Compact Solar Combisystem High Efficiency by Minimizing Temperatures Alexander Thür, Simon Furbo Technical University of Denmark DK-2800 Kgs. Lyngby, Denmark AEE INTEC A-8200 Gleisdorf, Austria E-mail: a.thuer@aee.at

REBUS Competitive solar heating systems for residential buildings Auxiliary energy: Natural Gas and Pellets Up to 50% of the energy consumption shall be covered by solar For existing and for new houses with little space for installation High degree of prefabrication and compactness Demonstration with one year monitoring Participants: Universities and Industry in DK, N, S, LT Period: 2003-2006

Background: IEA SHC Task 26 and ALTENER project: Solar Combisystems Good interplay between energy sources (auxiliary, collector) and demand (space heating, domestic hot water) Low return temperatures Good thermal stratification in the heat storage Low auxiliary temperature in top of heat storage Low heat loss from heat storage and technical equipment

Typical Solar Combisystem in Denmark No space heating solar storage => For small solar fraction Problems for condensing natural gas boiler: Low Flow/Power during space heating: 1 6 kw; 50 300 L/h High Temperature during domestic hot water preparation

Solar Combisystems with Natural Gas Burner Advanced Integrated Systems

Problem of Boiler Integration Specific boundary conditions of the combination solar thermal + condensing natural gas boiler For high efficiency because of internal bypass most condensing natural gas boilers need a minimum flow rate of: 450 600 ltr/h => Space heating demand: 6 kw => T = 12 9 K => Exhaust gas condensing temperature: 57 C For high performance a solar heating system needs lowest operating temperatures for the collector: => lowest return temperatures required BUT: Low temperature radiator heating system => large T => low flow Space heating system => Space heating: 6 kw and T = 50/30 => 260 ltr/h

New Concept Condensing Natural Gas Boiler High Peak Power: ~ 30 kw Fast reacting => Hot water preparation by the gas boiler is possible => NO Standby volume at high temperature 60-65 C => Lower tank heat losses => Larger effective solar heat storage volume => Keeping stratification => Higher collector efficiency and gain

New Concept System efficiency Use auxiliary standby volume at low temperature level if NO solar energy in the tank is available. => Long running periods of the gas boiler => Minimizing Start/Stop Losses and Emissions => Low forward temperature for space heating => High condensation rate =>! Reduction of pipe losses between boiler and tank! =>! Reduction of pipe losses between tank and SH mixing valve! 25-50 C 15-30 C

Energy [kwh] TRNSYS Simulations 17000 16000 15000 14000 13000 12000 11000 10000 9000 8000 Solar Combisystem 6m 2 collector area and 300/90 ltr buffer tank Set = 65 C Ref Set = 65 C Solar +83% Set = flex Solar Set = 65 C Ref Set = 65 C Solar Set = flex Solar Pipe losses Solar loop losses Tank Losses Total energy demand Collector gain Boiler Energy Input Energy Use Increased energy savings due to advanced operation strategy: 6m 2 / 300 ltr tank: + 83% 20m 2 / 1000 ltr tank: + 33%

Developed Compact Natural Gas Solar Combisystem Units from Metro Therm A/S Solar Store Unit Technical Unit 4 Domestic Hot Water HW (P6) (V5) S (P4) Space Heating M 1 CW (V3) S M (V4) Radiators (V2) M Floor Heating 2 (P3) Boiler 3 5 (P2) (P1) S (V1) Collector Loop

Developed Compact Natural Gas Solar Combisystem Units from Metro Therm A/S Solar Store Unit Technical Unit 4 Domestic Hot Water HW (P6) (V5) S (P4) Space Heating M 1 CW (V3) S M (V4) Radiators (V2) M Floor Heating 2 (P3) Boiler 3 5 (P2) (P1) S (V1) Collector Loop

Equivalent systems,... but looking quite different!!

Main characteristics Units are built as 60 x 60 cabinets including all components Maximized prefabrication => Easy and fast installation, avoiding mistakes Solar thermal system can be added later because technical unit can be operated without the solar tank as well Flexibility for small and large solar heating systems Flexibility for using different condensing gas boilers High efficiency due to ONE controller with tuned control algorithm: Good operating conditions for the boiler Good operating conditions for the collector Low return temperatures from: space heating and domestic hot water preparation system

Technical Unit Natural Gas Boiler

Solar Store Unit

Solar Store Unit Top of the tank with two small holes for temperature sensor sockets. Vacuum panel at the front of the tank.

Solar Store Unit Measurement results at SERC: ~ 2 W/K

Rebus Pellet at SERC / SE 1) 80 ltr Auxiliary Tank 2) DHW & SH Unit 3) Pellet Boiler 4) Solar Unit 5) Solar Tank

Old: New: Demonstration House 3 Persons, 3 Floors, 172m 2 gross area Boiler: 22 kw (1990, non condensing) Domestic Hot Water Tank: 50 Liter Boiler: 24/28 kw (2006, condensing) Solar tank volume: 360 ltr Collector area: 6.75 m 2 (5 x Velux S08)

Demonstration House Boiler Efficiency (LHV): 91 100 % Hydraulic Efficiency: 88 95 % COP = (SH+DHW) / Gas Consumption DHW circulation losses: <10%of DHW consumption Energy [kwh] 3200 2800 2400 2000 1600 1200 800 400 0 Oct 06 Nov 06 Dec 06 Jan 07 Feb 07 Mar 07 Apr 07 May 07 160% 150% 140% 130% 120% 110% 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Efficiency [%] Solar Gain [kwh] Natural Gas Consumption [kwh] Space Heating [kwh] Domestic Hot Water-Consumption [kwh] Domestic Hot Water-Circulation [kwh] Electricity [kwh] Boiler Efficiency [%] Natural Gas - COP [%] Hydraulic Efficiency [%]

Demonstration House Calculation of Energy Savings COP = (SH+DHW) / Gas Consumption 140% 130% 120% 110% COP [%] 100% 90% 80% 70% 60% 50% 0 500 1000 1500 2000 2500 3000 3500 4000 Monthly Load for Space Heating + Domestic Hot Water [kwh] Demonstration Solar Combisystem Demonstration Old Heating System Polynomisch (Demonstration Old Heating System)

3500 3000 2500 2000 1500 1000 500 0 Demonstration House Energy Savings: 368 kwh/m 2 Solar Gain: 217 kwh/m 2 COP SCS: 100% COP old: 86% Energy Savings per Month 140 120 100 80 60 40 20 0 Energy [kwh], Total Energy [10kWh] 10.2006 11.2006 12.2006 01.2007 02.2007 03.2007 04.2007 05.2007 Total [10 kwh] COP [%] Natural Gas Consumption old [kwh] Heat Load [kwh] Natural Gas Consumption SCS [kwh] Energy Savings [kwh] COP SCS [%] COP old [%]

Demonstration House Energy Savings: 368 kwh/m 2 Solar Gain: 217 kwh/m 2 COP SCS: 100% COP old: 86% Month Heat Load (SH+DHW) COP old COP SCS Natural Gas Consumption old Natural Gas Consumption SCS Energy Savings Energy Savings Solar Gain [kwh] [%] [%] [kwh] [kwh] [kwh] [kwh/m 2 ] [kwh/m 2 ] 10.2006 1256 88,2 99,2 1424 1266 158 23 21 11.2006 2068 86,5 96,4 2388 2146 242 36 10 12.2006 2127 86,4 94,8 2461 2244 217 32 4 01.2007 2635 85,4 93,2 3086 2828 258 38 4 02.2007 2782 85,1 94,2 3268 2953 315 47 9 03.2007 2226 86,2 105,2 2582 2116 466 69 46 04.2007 1445 87,8 123,9 1646 1166 480 71 70 05.2007 775 84,1 134,9 922 575 347 51 53 Total 15313 86,1 100,1 17776 15294 2482 368 217 Measured Natural Gas consumption: Old SCS Summer cons. 7/07-05 30/9-06 ( 85 days) Old: 1,509 kwh Summer cons. 7/07-06 30/9-07 ( 85 days) SCS: 318 kwh

Demonstration House Energy Savings: 681 kwh/m 2 Solar Gain: 483 kwh/m 2 COP SCS: 104% COP old: 84% Month Heat Load (SH+DHW) COP old COP SCS Natural Gas Consumption old Natural Gas Consumption SCS Energy Savings Energy Savings Solar Gain [kwh] [%] [%] [kwh] [kwh] [kwh] [kwh/m 2 ] [kwh/m 2 ] 10.2006 1256 88,2 99,2 1424 1266 158 23 21 11.2006 2068 86,5 96,4 2388 2146 242 36 10 12.2006 2127 86,4 94,8 2461 2244 217 32 4 01.2007 2635 85,4 93,2 3086 2828 258 38 4 02.2007 2782 85,1 94,2 3268 2953 315 47 9 03.2007 2226 86,2 105,2 2582 2116 466 69 46 04.2007 1445 87,8 123,9 1646 1166 480 71 70 05.2007 775 84,1 134,9 922 575 347 51 53 06.2007 300 62,0 230,8 484 130 354 52 56 07.2007 160 50,0 800,0 320 20 300 44 55 08.2007 180 56,0 720,0 321 25 296 44 55 09.2007 500 75,0 142,9 667 350 317 47 50 Total 16453 84,1 104,0 19568 15819 3749 555 433 Heating Degree Days: -25%!!! E S T I M A T I O N!

Demonstration House: Old <=> New Domestic Hot Water - Temperature Difference: - 35% Domestic Hot Water Consumption: - 20% Electricity Consumption: - 5% Space Heating - Temperature Difference: + 35% 140% 130% 120% 110% 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 eta_boil [%] COP [%] eta_hyd [%] DHW [kwh/d] DHW_dT [K] SH_dT [K] Electr. [kwh/d] Efficiency [%] 01 2005 02 2005 03 2005 04 2005 05 2005 06 2005 07 2005 08 2005 09 2005 10 2005 11 2005 12 2005 01 2006 02 2006 03 2006 04 2006 05 2006 06 2006 07 2006 08 2006 09 2006 10 2006 11 2006 12 2006 01 2007 02 2007 03 2007 04 2007 05 2007 Energy [kwh/d], Temperature Difference [K]

110% Boiler Efficiencies Solar Combisystem AUT: 102.1% / 18,688 kwh/a Conventional House DK: 96.3% / 29,965 kwh/a Boiler Efficiency [%] 105% 100% 95% 90% 85% 99.0% 94.6% 80% 0 1000 2000 3000 4000 5000 Monthly Load for Space Heating + Domestic Hot Water [kwh] Solar Combisystem - AUT Demonstration Solar Combisystem - DK Conventional House DK

CONCLUSIONS A new natural gas/solar heating system for high solar fraction was developed. High efficient system of boiler and solar heating system due to low temperature strategy. High energy savings in demonstration house were documented. Huge potential of reduction of DHW circulation losses. Potentials for improvements: Reduction of DHW heat demand with flexible tap temperature. Control strategies for low space heating return temperatures. Simplification of the system. We have to solve the problem of: HOW TO USE THERMOSTAT VALVES HOW TO ADJUST HYDRAULIC SYSTEMS

New Steps towards Compact Solar Combisystems in Scandinavia Thank you for your attention!