CHAPTER 4 EVALUATIONS FOR THE RETROFIT OF THE EUROPEAN RESIDENTIAL
4.5 Redevelopment of the HVAC system – methods
4.5.1 Configuration 0
The standard, assumed for the conditions before the redevelopment of the HVAC system, is a regular gas-fired boiler for heating and the generation of the DHW. No renewable resources are involved and none solar collector systems is consider as integration for the energy demand for DHW. According to the cooling energy demand, it has been satisfied by the means of single –zone air conditioning split- systems, technical features are shown in
Table 4.40.
COEFFCIENTS OF CONVERSION INTO PRIMARY ENERGY Thermal Energy by fossil fuels
Solar thermal Energy Thermal Energy by pellet combustion
Electrical energy
1 kWht >> 1.1 kWhp 1 kWht >> 0 kWhp 1 kWhe >> 0.3 kWhp 1 kWhe >> 2.3 kWhp
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For every case study a centralized heating systems has been considered, while the cooling energy demand is provided by several units placed in the occupied zones of the building. In order to esteem correctly the effect of the plant redevelopment, in the configuration 0 also a VMC has been considered, equipped with a heat recovery device with an efficiency of 50%.
Table 4.40. Technical features of air conditioning system
Table 4.41. Technical features of regular gas-fired boiler
The technical features of the boiler are presented in Table 4.41. To meet the energy demands of every case study one or more boilers have been considered in a parallel functioning. Proper value for the delivery and emission efficiency of the plant have been considered. This configuration considers a standard boiler, without any water tank, and radiators so the delivery and emission efficiency has been set to 0.94511[8]. Regarding the cooling energy demand a delivery and emission efficiency value equal to 0.955 has been assumed, considering the use of single zone air conditioning devices.
4.5.2 Configuration 1
The first configuration considered for the redevelopment of the HVAC system is an integrated multi- energy plant where several energy generator are combined together to supply the heating and cooling energy demand. The idea is to use every source until it is the most convenient in terms of energy efficiency. The combination of an air-water heat pump with a gas condensing boiler allows the first to
11 The standard UNI TS 11300:2 gives proper indication on the way the efficiency values of emission, regulation
and energy delivery should be evaluated.The indicate value cames from the standard procedure.
AIR CONDITIONING SPLIT-SYSTEMS 125 R WDD
Declared power kW
Minimum air flow m3/h Average air flow m3/h Maximum air flow m3/h Electrical power W 2.7 330 390 450 18
GAS FIRED REGULAR BOILER 30/130 TS
Thermal power kW
Lower thermal power kW
Efficiency @ 100% Efficiency @ 30%
Declared standard efficiency (CEE 92/42) NOx Class Electrical power W 29,4 11,7 93,1% 91,7% *** 3 180 HEATING
Max operative pressure bar Max opertaive Temperature °C Bolier water capacity l Heating temperature regulation °C Pressure bar 3 85 15 40/80 1 DHW
Maximun pressure bar Water flow EN 625 l/min
Water flow Dt 30°C l/h DHW Boiler capacity l 7 18,8 700 130
163 work until the external conditions (dry bulb air temperature and relative humidity) guarantee an efficient functioning, then the latter is called in an independent or combined functioning searching for the minimum primary energy consumption.
The technical features of the condensing boiler used in the analysis are presented in Table 4.42 for the cases 3 and 4 and in Table 4.43 for the case studies 1 and 2. The technical feature of the air-water heat pump used in the models are shown in Table 4.44. The small one is used in case 1 and 2 and the second one in case 3 and 4. When it was necessary due to the increasing in the energy demand two or three devices have been considered in combined functioning. Radiant floor panels have been chosen as heating delivery devices for all the case studied, delivery and emission efficiency value has been set equal to 0.988.
Solar thermal collectors have been considered as heat provider for the DHW generation. It has been considered the possibility of providing, with solar energy, an integration to heating energy demands as well. But on the basis of previous analysis, that seemed not to be convenient. In fact, the poor contribution to the heating energy supply don’t justified the complexity introduced in the plant by the connection of the solar system within the heating section. The technical features about the solar collectors are resumed in Table 4.45, while the parameters regarding their efficiency are presented in Table 46.
Table 4.42. Tecnical features of the condensing boiler (case 3,4)
Table 4.43. Tecnical features of the condensing boiler (case 1,2)
Table 4.44. Technical features of the air-water heat pumps
HP012 - R410A HP033 - R410A Compressor frequency [Hz] 30 110 30 120
GAS FIRED CONDENSING BOILER ME 100
Thermal power kW
Lower thermal power kW
Efficiency @ 30%/100% (80-60) Efficiency @ 30%/100% (50-30) Declared standard efficiency (CEE 92/42) NOx Class
Electrical power W
Max operative pressure bar Max opertaive Temperature °C Bolier water capacity l Heating temperature regulation °C
Pressure bar 93.6 (2x46.8) 10.5 96.9% / 97.5% 109.0% / 106.7% **** 5 360 3.5 85 4.6 20/80 1
GAS FIRED CONDENSING BOILER ME 35
Thermal power kW
Lower thermal power kW
Efficiency @ 30%/100% (80-60) Efficiency @ 30%/100% (50-30) Declared standard efficiency (CEE 92/42) NOx Class
Electrical power W
Max operative pressure bar Max opertaive Temperature °C Bolier water capacity l Heating temperature regulation °C Pressure bar 33.8 3.7 92.0% / 97.2% 106.3% / 106.8% **** 5 140 3.5 85 4.6 20/80 1
164
Cooling @ 35°C air 12/7°C water
Cooling power [kW] 3,1 11,3 6,1 32,2 Compressor auxiliary energy [kW] 0,6 3,1 1,4 10,9 Fans auxiliary energy [kW] 0,16 0,16 0,32 0,32 Pumps auxilay energy [kW] 0,07 0,07 0,31 0,31
EER 3,78 3,49 3,22 2,91
Water flow [kg/h] 525 1946 1056 5545
Air flow [m3/h] 7000 7000 14000 14000
Cooling @ 35°C air 23/18°C water
Cooling power [kW] 4,0 15,8 12,8 44,5 Compressor auxiliary energy [kW] 0,6 3,2 2,1 11,6 Fans auxiliary energy [kW] 0,16 0,16 0,32 0,32 Pumps auxilay energy [kW] 0,07 0,07 0,31 0,31
EER 5,20 4,65 5,23 3,76
Water flow [kg/h] 696 2721 2204 7663
Air flow [m3/h] 7000 7000 14000 14000
Heating BT @ 40/45°C e 7°C ext.air
Heating power [kW] 3,0 11,9 9,6 35,8 Compressor auxiliary energy [kW] 0,7 3,3 2,3 10,9 Fans auxiliary energy [kW] 0,16 0,16 0,32 0,32 Pumps auxilay energy [kW] 0,07 0,07 0,31 0,31
COP 3,20 3,41 3,46 3,23
Water flow [kg/h] 511 2049 1657 6165
Air flow [m3/h] 7000 7000 14000 14000
Heating BT @ 30/35°C e 7°C ext. air
Heating power [kW] 3,2 12,5 10,1 36,4 Compressor auxiliary energy [kW] 0,6 2,7 1,9 9,0 Fans auxiliary energy [kW] 0,16 0,16 0,32 0,32 Pumps auxilay energy [kW] 0,07 0,07 0,31 0,31
COP 4,00 4,33 4,31 3,97
Water flow [kg/h] 542 2153 1739 6268
Air flow [m3/h] 7000 7000 14000 14000
Table 4.45. Technical features of the solar collectors VACUUM HEAT PIPE SOLAR COLLECTOR
Number of tubes 20 Fluid content 0.9 l
Diametre of tubes 65 mm Flow rate regulation 60 - 250 l/h Glass thickness 1.7 mm Tested flow rate 160 l/h
Length 2.0 m Absorber element copper sheet
Width 1.452 m Absorber lengh 1.730.0 m
Heigth 0.165 m Absorber width 58.0 mm
Coefficient of absorption > 95% Absorber thickness 0.15 mm
Coefficient of emission < 5% Selective covering titanium oxide
Gross area 2.904 m² Max operative temperature 150°C
Aperture area 2.270 m² Max operative pressure 6 bar
Absorption area 1.984 m² Absorption element copper sheet
Weight 49.5 kg
Table 46. Parameters of performance of the solar collectors
Absorber area Aperture area Gross area
ᶯ
0 optical efficiency 0.812 0.710 0.555a1 (W/m2K2) 1.43 1.25 0.98
165 Heat storage have been need to collect the thermal energy given by the different generators. In the case 1 and 2 a single storage tank has been considered. It is a storage with a capacity of 500 litres, provided with two coiled heat exchangers, one placed in the upper part of the tank and linked to the boiler and the second placed in the bottom part of the tank and connected to the solar system. Three ports (a port refers to a pair of inlet and outlet) allow the connection to the heat pump and to the delivery circuits for heating and DHW. in case 3 and 4 three storages are implemented in the model, one dedicated to the heating section and two to the DHW generation.
The storages implemented in the case studies 3 and 4 are more complex. The storage for the heating section of the plant has a capacity of 800 litres, and it has not provided with heat exchangers. The boiler circuit as well as the one of the heat pump is connected to the tank by the means of a port, and also the pipes of the heating circuit are direct connect to the storage.
The tanks dedicated to the DHW generation have a capacity of 2000 litres each. They have a port connected with the boiler and a coiled heat exchanger connected to the solar collectors circuit. A second coiled heat exchanger is used to provide the DHW generation. Water from the aqueduct comes in from the bottom of the storage and trough the coil crosses all the tank until the outlet, where it is mixed with a proper quantity of cold water and the delivered to the users.
Controlled mechanical ventilation has also been implemented, in order to guarantee a proper quality of the indoor environment, the air flow change was set to 0.56 V/h. Heat recovery systems have been implemented with an efficiency of about 90%.
4.5.3 Configuration 2
The second configuration a differs from the former in the choose of the heat pump. A water heat pump has been selected and the cooling energy demand has been satisfied by the means of an air-water chiller. Technical features of the selected machines are provided below.
With the exception of the choose of the heat pump and the cooling devices the rest of the plant is equal to the configuration number 1.
Table 4.47. Technical features of the chiller used in Cases 1 and 2 CHILLER 008 - R410A
Cooling @ 35°C air 12/7°C water
Cooling power [kW] 7.8 auxiliary energy [kW] 1.98
EER 3.95
Water flow [kg/h] 590
Air flow [m3/h] 6300
Table 4.48. Technical features of the chiller used in Cases 3 and 4 CHILLER 020 - R410A
Cooling @ 35°C air 12/7°C water
Cooling power [kW] 34.4 auxiliary energy [kW] 5.6
EER 6.15
Water flow [kg/h] 5900 Air flow [m3/h] 13500
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Table 4.49. Technical features of the water heat pump used in Cases 1 and 2 WATER HEAT PUMP 040 - R410A
Heating power 40/45°C water 10/7°C water [kW] 12.56 auxiliary energy [kW] 3.14
COP 4.01
Water flow condenser [kg/h] 2838 Water flow evaporator [kg/h] 2746
Table 4.50. Technical features of the water heat pump used in Cases 3 and 4 WATER HEAT PUMP - R410A
Compressor frequency [Hz] 50 Heating @ 40/45°C water 10/7°C water
Cooling power [kW] 55 auxiliary energy [kW] 13
EER 4.2
Water flow condenser [kg/h] 6500 Water flow evaporator [kg/h] 6300
4.5.4 Configuration 3
The configuration number 3 considers a gas condensing boiler as heat generator. Unlike the former solutions, this plant is not equipped with any heat pump and as heat delivery systems fan coils have been chosen instead of radiant panels, so the delivery and emission efficiency value is equal to 0.955. During the heating season the boiler set temperature is fixed to 70 °C, and the operative temperature of the fan coils is set equal to 60 °C. Technical features of the boilers are provided in Table 4.42 and in Table 4.43.
4.5.5 Configuration 4
The configuration number 4 is identical to the number 3. The only difference is represented by the heat delivery facilities that in this solution are traditional cast-iron radiators; the delivery and emission efficiency value is equal to 0.945. As in the former configuration, during the heating season the boiler set temperature is fixed to 70 °C, and the operative temperature of the fan coils is set equal to 60 °C.
4.5.6 Configuration 5
The last configuration analyzed is equal to the plant solution number 3. The difference between them is represented by the choice of a pellet fired boiler, technical features are provided in
Table 4.51 and in Table 4.52. According to the energy demand of each case study one or more boiler have been combined to meet the user needs.
The conversion of the energy supplied by the combustion of pellet into primary energy has been done considering a coefficient of 0.7. That means that for every kWh generated by the pellet fired boiler only the 70% have been considered renewable energy, the other 30% is converted as generated by fossil fuel [9]. Traditional cast-iron radiators have been considered and the delivery and emission efficiency value has been set equal to 0.945.
167 Table 4.51. Tecnical features of the pellet fired boiler (case 1,2)
Table 4.52. Tecnical features of the pellet fired boiler (case 3,4)