The test set up included façade integrated solar thermal collectors (see Chapter 01 and CH02-1.1.6) in order to collect additional renewable heating energy. The collected heating energy especially for winter months was reviewed in terms of effect on substitution potential. Moreover, this thesis inspects the potential of collected, stored and utilized energy in terms of sun space autarky and potential of surplus energy contribution for an adjacent residential family home. Nonetheless, the amount of net energy, that was required to run the collector and storage system, is to be considered and related to the amount of gained renewable energy.
Moreover, the ratio of required auxiliary energy and gained renewable energy is an expression of system efficiency. This section calculates gained and required auxiliary energy and determines the system efficiency of the tested experimental sun space.
159 Literature survey and empirical evaluation of thermal comfort in sun spaces
§ 2.10.1
Renewable Energy generated by sun space facades
Figure 2.71 plots the cumulated progress of generated solar thermal energy for 18 months with weekly interval. The histogram additionally plots the summed yield for every month. With subject to system fall outs or maintenance April 2015 generates with considerable distance to the rest the highest monthly yield of 281 kWh. April is followed by May 2015 with 147 kWh and June 2014 with less than the half, res- pectively 125 kWh. Autumn months like September and October encounter demon- strable periods of system fall out and asses 77 and 33 kWh, and 42 and 28 kWh respec-tively. From midsummer 2014 to 2015 and from spring 2015 to 2016 is generated 1.091 and 869 kWh respectively. Dynamic thermal simulation calculated a heating energy demand of approximately 1.600 kWh in order to provide sufficient energy for satisfactory operative temperature of >20°C between 5 to 10 PM from October to April.
Thus, the overall opinion of the author beside the documented monthly yields is, that the system dConsidering September (also see Appendix B.8), glazing east and north cumulate frequencies of 305 and 333 hours respectively, what equals 44 and 48% of hours in total. That frequencies demonstrably lowers, when focus is set on evening hours. For the 5 to10 PM time frame glazing east and north simply provide temperature differences >23K for 12 and 14% of hours respectively. esign for energy generation is designed sufficiently.
Figure 2.72 plots weekly generated cumulated solar thermal energy and monthly sums. Additionally the histogram illustrates the cumulated progress of weekly consumption of the renewable energy. It becomes obvious, that right from the start in June 2014 demonstrably more energy was generated than consumed. That is strongly related to the fact, that energy generated in summer month is not con-sumed since demand is zero. Opposed to that, shows the parallel progress of energy generation and consumption from November 2014 to end of February 2015 that the few generated renewable en- ergy was consumed immediately.Opposed to the measured energy yield illustrated in Figure 80 the impression of the author during experimental test set up period was, that without too many fall out periods the system normally generates enough energy (< 1.600 kWh/a) during the year in order to provide 1.060 hours of satisfying thermal comfort.
FIGURE 2.72 Cumulated weekly heating energy consumption and monthly sums vs. cumulated weekly solar thermal yield
High system efficiency of course implies the implementation of a loss free seasonal thermal storage. Thus, the overall opinion of the author beside the documented monthly yields is, that the system design for energy generation is designed sufficiently. Figure 81 plots weekly generated cumulated solar thermal energy and monthly sums. Additionally the histogram illustrates the cumulated progress of weekly consumption of the renewable energy. It becomes obvious, that right from the start in June 2014 demonstrably more energy was generated than consumed. That is strongly related to the fact, that energy generated in summer month is not consumed since demand is zero. Opposed to that, shows the parallel progress of energy generation and consump- tion from November 2014 to end of February 2015 that the few generated renewable energy was consumed immediately.
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§ 2.10.2
Net power consumption as auxiliary energy
Similarly, the parallel but off-set progress of generation and consumption between March and May 2015 demonstrates, that consumption is linked to generation, but more interestingly, either much of the energy generated got lost by transmission losses of the 300L buffer tank and the system itself or was provided simply by passive solar gains. Likewise the figure before, in April was measured the highest consumption. However, in the last month of the winter period and transitional spring month are simply 90 kWh consumed towards 281 kWh generated. That equals nearly one third. Similarity is verified for September 2014, where 77 kWh are generated but solely 20 kWh consumed and for February with 42 and 4 kWh respectively. Auxiliary required power for distribution components within the system can be identified as follows:
• solar thermal circuit pumps ( 2x primary, 2x secondary) : each 3 Watts, • solar thermal circuit electromagnetic valves (south, west) : each 5 Watts, • floor heating pump (1x) : 3 Watts, • floor heating circuit servos (1x south, 1x west) : each 2 Watts
Valves and servos are normally closed power-off, hence they consume energy exclusi- vely when pumps are in action. In Figure 2.73 required auxiliary energy is plotted against the consumed heating energy.
The graph clear-cut demonstrates, that required auxili-ary energy for solar thermal circuit pumps, electromagnetic valves, floor heating pump and the floor heating circuit servos do not fall into worth mentioning account. Thus, the generated solar thermal energy can be considered to be the effective energy gain for further space heating.
§ 2.10.3
Ratio–autarky ratio
It was not possible to verify an autarkic operation defined by 1.060 hours of sufficient thermal comfort exclusively by passive solar gains and additional renewable energy during 5 to 10 PM form October to April by the experimental test set combined solely with a sensible heat storage. That was reasoned by too many system fall out during two years of observation. Autarkic operation was furthermore hardly feasible since a sensible water storage provided energy for rarely more than four days.
§ 2.10.4
Summary
Yet, an exploratory calculation of monthly yields revealed an feasible approximately annual yield of 1.600 kWh by this installed experimental collector system at location Bissendorf.
Nonetheless, opposed to the observed days, the author is convinced, that the system without any fall out and in combination with a seasonal loss free storage is capable to realize satisfactory thermal comfort for 1.065 hours.
However, the system is limited in capacity in terms of renewable energy generation. The specific test set up configuration is expected not to be feasible for any surplus heating energy contribution for residential heating energy substitution.
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§ 2.11
Summary
Theoretical literature research and empirical evaluation of thermal comfort in sun spaces results in manifold findings at the end of this chapter.
Literature review figured out, that improvements of steady-state analysis models to dynamic hourly weather data based models do justice to thermally rapidly reacting sun spaces. Moreover, simulation tools developed in respect to absorption and reflection terms and in regard of modelling vertical striation. Review revealed an overestimation of overheating and cooling loads and diametrically an underestimation of heating demand.
Moreover, the focus of effective sun space planning moved to thermal mass and absorption ability of the separation element as well as thermal mass of floor and massive walls. Thermal mass to façade ratios additionally established as designing tools for sun spaces. Essentially, the question raised to clear-cut define actual utilization behaviour and daily occupation time. Both significantly influence and rule required and recommended thermal mass quality in order to regulate overheating and controlled heat return.
Further, required opening areas are discussed in order to enhance cooling by natural ventilation. Diverse authors limit effective opening to maximum 30% of the entire sun space envelope.
Sun spaces in general have been detected and promoted to be eligible to reduce daily temperature amplitudes, temperature swings and heating energy for adjacent zones and residential buildings respectively. Nonetheless, several authors pointed out, that the effect is significant for the actual adjoining zone, but however, much less for an entire building. Thus, energy saving potential considerably depends on the size of the adjacent zone and its area-wise fraction on the entire net-area.
Sun spaces absolutely save more heating energy for poor insulated estates, whereas they relatively demonstrably improve energy performance of modern residential homes with supreme energetic quality standard.
PMV and PPD models cannot be applied to sun spaces, since assessments of empirical data causes unreliable and unreasonable results. Further evaluation based on adap- tive comfort algorithms and calculation of cumulative frequencies of dry bulb and operational temperature, striation and radiation asymmetries as well as progress of radiant temperature as indication of inertia.
Inspection of resulting temperature recovered, that the lower set point limit of 20°C was accomplished solely during midsummer months. Thus, solely by passive solar gains, comfort limit majorly was achieved during June, July and August. However, during November, December, January and partly February the lower set point limits was hardly attained. Nonetheless, September and May and fractions in April showed very well balanced proportions of complied set point limits and overheating, either in respect to cumulative frequencies of resulting temperature or in terms of adaptive comfort bandwidths. April was observed to either lack considerable fractions of satis- fying operational temperature, but rather to encounter demonstrably high fractions of hours with overheating. As a conclusion for April, the number of outliers raised while overheating raised.
This first findings allow to draw the conclusion, that prediction of sun space thermal comfort for the experimental test set up was extremely difficult.
The empirical inspection revealed, that diurnal natural ventilation with area-intensive fold-works in midsummer and on sunny spring days was not effective in terms of space cooling. Dry bulb temperature always remained above external temperature with an off-set of 6 to 10 Kelvin. Solely night cooling lowered dry bulb temperature of the internally shaded experimental sun space for 8 to 21 Kelvin.
The empirical evaluation revealed, that cumulative frequencies of hours with satisfying operational temperature during the preferred occupation time between 5 to 10 PM mostly exceed those representing an entire day perspective. That is true for the period March to October, however, except August. Thus, the evening hours established by evaluation to be the most enjoyable once. Interestingly, in the context of adaptive comfort bandwidths evaluations, mostly the south flank of the sun space performed better than the west flank, except during September and October.
Comfort charts, which plot operational temperature against relative humidity, showed, that the major fraction of hours between March and October located in the comfortable or still-comfortable field. On the contrary, the charts diametrically elaborated, that relative humidity very often exceeded 80% during November, December and January. Beside unsatisfactory operational temperature, these months encountered a clammy space environment.
The evaluation of mean radiant temperature in relation to external temperature lead to interestingly insight in respect of sun space specific inertia. During winter months like January, February and March thermal mass tended to slightly but persistently charge. That resulted partly in daily compensation of irradiation fluctuations and in a steady raise of dry bulb temperature. This analysis recovered, that in particular in April inertia
165 Literature survey and empirical evaluation of thermal comfort in sun spaces
was sufficient to compensate on weekly level. However, during May and November, the thermal mass tended to discharge but managed to provide better balanced thermal comfort. Nonetheless, November was observed as month of significant discharge of thermal mass without any positive influence on resulting temperature. We investigated August when limit of positive effect of thermal mass capacity was reached.
Floor temperature was inspected to be most of the year too cold, exceptionally in June, July and August, when local discomfort resulted oppositional from too warm floors. On the contrary, north and east glazings, which predominantly lack from direct irradiation, reasoned radiation asymmetries with facing surfaces, except during midsummer months. North and west roof glazings as well as vertical glazings either provided too cold or too warm surface temperature. This fact resulted in massive and persistent radiation asymmetries during winter months (November to April) or in particular during midsummer (June to August).Vertical striation in the torso-to-head height between 1,10 m to 1,70 m above floor was detected to be a major and dominant local discomfort phenomenon typical for the experimental test sun space during the entire year.
Finally, a long term evaluation of operational temperature of the test sun space substantiated a principle lack of thermal comfort provided both by solar gains and additional sporadic floor heating during from November until March.
Analogously, in terms of overheating the most degree hours were detected in June and August for thesouth flank, what changed towards the west flank in October. Nonetheless, the fewest degree hours were observed for both sun space flanks in September and October.
167 Literature survey of façade integrated renewable energy collector technology