S O M A M O H A M M A D I 13 MARCH 2014

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Hilda Wilkerson
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1 CONVERSION OF EXISTING DISTRICT HEATING TO LOW-TEMPERATURE OPERATION AND EXTENSION OF NEW AREAS OF BUILDINGS S O M A M O H A M M A D I 13 MARCH 2014

2 Outline Why Low - Te mperature District Heating Existing District Heating Networks By-pass Application in existing d istrict heating Networks District Heating Networks S imulation Re a l - Life District Heating Network 2

3 Why Low-Temperature District Heating B e ca use of incre asing the n umber of low-energ y and e nergy re n ovate d b u ildings B e cause of the growing d e mand for incre asing the share of re n ewable energ y s ources and waste heat I ntroducing 4th generation of District Heating is key (Supply and return te mperature 55 C and 25 C re s p e ctively) Re d u ce Heat loss in District Heating Syste m I n cre a s e Combined h e at and Power plant, power generation capacity and Utilize dire ct flue gas condensation for waste heat re covery 3

4 Existing District Heating Networks In ord e r to implement low te mperature d istrict heating concept in existing n etwork, there are two situations needs to be considere d : Pe a k - h e at load periods/heating s e ason Low-heat load periods/non - heating s e ason 4

5 Peak-load periods P ro b lem : lowe ring the te mperature may ca use costumers dissatisfaction at p e ak-demand p e riods in ord er to p rov ide their s p ace heating d e m a n d. P ro p osed solutions: I n cre asing the supply te mperature at high-demand p e riods local te mperature b oosting. 5

6 Low-heating load periods Existing solution: Curre ntly By- p ass is applied in d istrict heating syste m. 6

7 Main disadvantages in Existing By-pass Higher Heat Loss in the networks Incre ased return flow te mperature Re d u cing Power ge n e ration capacity in combined h e at and p ower p lants The By- pass problem b e comes more critical when it comes to low - e n e rg y b u ildings as the s h are of h e at losses due to by-pass operation can be very h igh re lative to their heat demand. 7

8 Recent Studies in By-pass application By- p ass wate r re c irculation Network Design Return temperature Recirculated by-pass temperature Heat loss Reference scenario (Traditional DHN) 35.5C - 12,78 kw By-pass water recirculation (Summer time) 22C 44C 18 kw Double pipe line supply (Winter time) 22C - ** * * d o u b l e p i p e s u p p l y l e a d s t o t h e h i g h e s t n e t w o r k h e a t l o s s. H o w e v e r t h e c o n c l u s i o n rega rd i n g u s i n g d o u b l e p i p e c a n b e d ra w n a f te r f u r t h e r n e t w o r k t h e r m a l - e c o n o m i c o p t i m i zation. 8

9 Recent Studies in By-pass application U s e o f by - p ass in b athroom floor h e ating -Continuous by - p ass 1. Te chno-economic analysis of the use of by - p a s s flow in bathroom f loor heating for low energ y b u ildings 2. Modeling in house the space h e ating syste m Re s ults: 1. G u arantee lowering the h e at loss fro m the service p ipes 2. Increase the thermal comfo rt o u tside the h e ating season in b athroom thro ugh floor h e ating w it very limited o verheating p ro b lems 9

10 Alternative By-pass strategies Local te mperature b oosting of domestic hot wate r by means e lectrical heate r or heat pump L ocal heat s u p p ly f rom s olar thermal syste m in the summer time 10

11 District Heating Modeling The purpose of this study is: To develop a flexible tool to ca lculate hyd ra u lic and thermal b e h av ior of district h e ating n etwork. in ord e r to: F i n d i n g o p t i m a l s u p p l y t e m p e ra t u re i n a n ex i s t i n g n e t w o r k s a s a f u n c t i o n o f D H N h e a t l o s s, p u m p p o w e r d e m a n d a n d ret u r n t e m p e ra t u re fo r a ra n g e o f s u p p l y t e m p e ra t u re s. T h e m o d e l i s u s e d fo r d e f i n i n g l o c a l t e m p e ra t u re b o o s t i n g a s a l t e r n a t i v e s t ra t e g y fo r b y - p a s s a p p l i c a t i o n a n d at peak - l o a d p e r i o d s. 11

12 District Heating Modeling The model is developed in Matlab. It starts by developing a s implified model with a range of a s s u m ptions. The model is validate d by applying for an existing re al-life d istrict heating networks. 12

13 District Heating Networks Simulation The model is based on a pseudo-dynamic approach where as: T he flow and pre s s ure a re ca lculate d u s ing a static flow model. The te mperature is calculate d d ynamically d e p e n d ing on the flow velocity and several b oundary conditions like s oil and outside te m p e rature. Main Assumptions: The fluid pipe flow is one - d imensional Tu rbulent fluctuations are not considere d The network is fre e of leaka ge The fluid characte ristics like density and heat capacity are constant 13

14 Hydraulic Calculation G raph theory is consid ere d to be the b e st tool for network analysis The DH system is c o n s i d e re d as a c o l l e c t i o n of n o d e s c o n n e c t e d by d i re c t e d e d g e s ( p i p e s ). T he n e t w o r k g ra p h in a m a t r i x d a ta s t r u c t u re c o n t a i n i n g t h e i n c i d e n c e m a t r i xe s a n d M a t r i x A a s s o c i a t e s e a c h e d g e w i t h i t s p a i r of n o d e s. M a t r i x B d e s c r i b e s t h e l o ca t i o n of t h e e d g e s in e a c h c i rc u i t. Nodes Edges (Pipes) 14

15 Hydraulic Calculation K i r c h h o f f s c i r c u i t l a w s a r e a p p l i e d t o b u i l d t h e e q u a t i o n s d e s c r i b i n g t h e f l o w r a t e s a n d p r e s s u r e l o s s e s i n t h e n e t w o r k : T h e l a w o f c o n s e r v a t i o n o f m a s s : t h e t o t a l a m o u n t o f f l o w i n t o o n e n o d e i s e q u a l t o t h e t o t a l a m o u n t o f f l o w o u t o f i t : A V = 0 W i t h t h e f l o w v e c t o r V = { V 1, V 2,, V n } T h e l a w o f c o n s e r v a t i o n o f e n e r g y : t h e s u m o f a l l p r e s s u r e d i f fe r e n c e s a l o n g t h e e d g e s o f o n e c i r c u i t i s e q u a l 0 : B p = 0 W i t h t h e p r e s s u r e d i f fe r e n c e v e c t o r p = { p 1, p 2,, p n } * D a r c y - We i s b a c h e q u a t i o n i s u s e d fo r p r e s s u r e l o s s c a l c u l a t i o n. 15

16 Thermal Calculation Te m p e ra t u re p ro p a g a t i o n w i t h i n o n e p i p e : C o nve c t ive h e a t f l o w = Q K x = m x. h = m x. c p.t H e a t l o s s f l o w = d Q V = k. d x. ( T T soil ) δt m c p δt = m x. c p. δt δx. d x k. d x. ( T T soil ) T h i s p a r t i a l d e fe re n t i a l e q u a t i o n d e s c r i b e s t h e t e m p e ra t u re p ro p a g a t i o n i n s m a l l e l e m e n t. T h e n t h e f i n i t e e l e m e n t m e t h o d i s a p p l i e d t o s o l v e t h e e q u a t i o n a n d t o o b t a i n t h e t e m p e ra t u re p ro f i l e a l o n g t h e p i p e. 16

Real-Life District Heating Network The model consists of 31,356 Km of main pipework trace. There are 1.441 consumers in the model.

17 Real-Life District Heating Network The model consists of 31,356 Km of main pipework trace. There are consumers in the model. Each node has a load applied, which is calculated as the sum of the entire consumer loads connected to that node. There are 110 bypasses in the model. All bypasses are set on 65 C, and are assumed to have measuring tolerance on 2,5 C. To ensure accurate and fast calculation the network has been reviewed to eliminate short pipes and to combine adjacent pipes with the same dimension 17 Harlev DHN which is used for simulation of its DHN in TERMIS

18 Next Steps C o m p l e t e t h e s i m p l i f i e d m o d e l i n M a t l a b A p p l i e d m o d e l fo r a re a l - l i fe n e t w o r k a n d va l i d a t e t h e m o d e l O p t i m a l s u p p l y t e m p e ra t u re Te m p e ra t u re b o o s t i n g a s a l t e r n a t i v e s o l u t i o n fo r b y - p a s s a p p l i cat i o n 18

19 Thank You

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