New Steps towards Compact Solar Combisystems in Scandinavia

Transcription

1 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

2 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:

3 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

4 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; L/h High Temperature during domestic hot water preparation

5 Solar Combisystems with Natural Gas Burner Advanced Integrated Systems

6 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: 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

7 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 C => Lower tank heat losses => Larger effective solar heat storage volume => Keeping stratification => Higher collector efficiency and gain

8 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! C C

9 Energy [kwh] TRNSYS Simulations 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%

10 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

11 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

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

13 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

14 Technical Unit Natural Gas Boiler

15 Solar Store Unit

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

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

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

19 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)

20 Demonstration House Boiler Efficiency (LHV): % Hydraulic Efficiency: % COP = (SH+DHW) / Gas Consumption DHW circulation losses: <10%of DHW consumption Energy [kwh] Oct 06 Nov 06 Dec 06 Jan 07 Feb 07 Mar 07 Apr 07 May % 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 [%]

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

22 Demonstration House Energy Savings: 368 kwh/m 2 Solar Gain: 217 kwh/m 2 COP SCS: 100% COP old: 86% Energy Savings per Month Energy [kwh], Total Energy [10kWh] Total [10 kwh] COP [%] Natural Gas Consumption old [kwh] Heat Load [kwh] Natural Gas Consumption SCS [kwh] Energy Savings [kwh] COP SCS [%] COP old [%]

23 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 ] ,2 99, ,5 96, ,4 94, ,4 93, ,1 94, ,2 105, ,8 123, ,1 134, Total ,1 100, Measured Natural Gas consumption: Old SCS Summer cons. 7/ /9-06 ( 85 days) Old: 1,509 kwh Summer cons. 7/ /9-07 ( 85 days) SCS: 318 kwh

24 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 ] ,2 99, ,5 96, ,4 94, ,4 93, ,1 94, ,2 105, ,8 123, ,1 134, ,0 230, ,0 800, ,0 720, ,0 142, Total ,1 104, Heating Degree Days: -25%!!! E S T I M A T I O N!

25 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% eta_boil [%] COP [%] eta_hyd [%] DHW [kwh/d] DHW_dT [K] SH_dT [K] Electr. [kwh/d] Efficiency [%] Energy [kwh/d], Temperature Difference [K]

26 110% 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% Monthly Load for Space Heating + Domestic Hot Water [kwh] Solar Combisystem - AUT Demonstration Solar Combisystem - DK Conventional House DK

27 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

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