12th International Symposium on District Heating and Cooling

In addition, it can also be observed that among alltypes of buildings, apartment houses representsomehow the highest efficiencies which justify the mainfocus in this study. The displayed case applies for thevalues where the design temperature level is 80/60 ˚C.It can be concluded from other calculations that thehigher the design distribution temperature level, thelower the production efficiency. This conclusion is whatcould be expected considering the difference betweenthe average temperature and the ambient temperature;the larger this difference, the larger the losses.As shown in Table 1, the efficiency varies only between0.9784 and 0.9673. It can be concluded, compared tothe distribution loss values that the productionefficiency is not changing significantly even if thetemperature level is changed. As a conclusion it can besaid that the losses in the production are relatively lowfor bigger houses but increasing quite rapidly forsmaller buildings.Table 1 Efficiency of DH production system for differentdesign temperature levels.Kind ofbuilding 80/60 70/55 55/45 35/28Apartmentblocks 0,9776 0,9778 0,9780 0,9784Office building 0,9729 0,9732 0,9735 0,9740Hotel andrestaurantbuilding 0,9701 0,9703 0,9706 0,9709Educationalbuilding 0,9676 0,9678 0,9681 0,9685Hospitalbuilding 0,9773 0,9775 0,9777 0,9780The quality of the insulation of the storage tank will alsoinfluence the production efficiency. Manufacturesshould follow the standard pr EN5044:2005 [7] in orderto calculate these losses. Losses from storage tanksshould be considered closely in practice, and tankswith relative high losses should be considered forreplacement or to be replaced by direct heatexchangers for DHW.Distribution efficiencyFirst the system for the distribution of tap water isanalyzed. In this case, the building includes acirculation loop (in small dots Figure 2) which goesfrom the storage tank, to the third floor and thedistribution branches (in bigger dots in Figure 2) whichdeliver DHW from the central loop to the consumer.The water temperature in the circulation loop isassumed to be at 60 ˚C throughout the whole year. Thebiggest share of the losses come from the circulationThe <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, Estonia241loop ranging up to 35 % of the total losses from thetotal distribution system. This loss is related to the factthat the water that remains in the distribution pipelinesrepresents 5% of the total losses per flat.For this calculation it is assumed that the pipelineshave insulation which a loss of 0.3 W/m∙K (thepipelines are considered to be according to thecategory ―installed after 1995‖ in [5]). In this calculationthe losses due refilling the pipes with hot water areincluded. This heat could be considered as recoverableloss for space heating during the heating season but inlack of a special national annex all the losses related tothe distribution of DHW should be considered as ―nonrecoverable‖. These losses are not related to thedemand for heat and will consequently be lost or resultin increased room temperatures.When it comes to SH, the losses are related to thetemperature difference in the non-heated areas wherethe water goes through. These losses are relatively lowcompared with tap water since most of these lossesare considered to be recoverable. The values used aretabulated in the EN standard [5].The percentage of recoverable losses is the cause ofthe higher efficiency for distribution of space heatingwhich ranges 0.99, whilst the efficiency for distributionof DHW is in thee range of 0.60.Emission efficiency in the roomsIn this case, domestic hot water is not considered tocontribute to the room heating since the losses fromthe discharge cocks are considered negligible.In case of space heating a difference has to be madebetween floor heating and radiator heating when itcomes to the efficiency calculations.Floor heating is by its nature emitted at lowertemperature, which has an effect on the stratificationefficiency since the lower the temperature level, thehigher this η str. By definition in [6] the stratificationefficiency of floor heating is 1 whilst this parameter forradiators goes down to 0.91 on the 80/60 distributionsystem. This value is combined with the efficiencyvalue of 95 % due to the positioning of the radiators ona normal external wall. Together these values make atotal room efficiency of 0.93.However, a regulation with PI controllers for theradiators delivers an efficiency of 0.97 while the samecontroller remains at 0.95 for floor heating.In case of the embedded floor heating efficiency theefficiency is 0.93. Since it is considered to be normalinsulation layer according to EN 1264, it results in aη emb of 0.95, the combination results in η emb of 0.94.Due to these three parameters, floor heating all in allhas a room efficiency of 0.90 and radiators of 0.88.