UNIVERSITY OF COPENHAGEN FACULTY OF HEALTH AND MEDICAL SCIENCES
Cooling of recirculated water for floor cooling GreenLiv report Rikke Koch Hansen & Bjarne Bjerg
April 2018
Table of content INTRODUCTION ................................................................................................................. 3 EFFECT OF FLOOR COOLING SYSTEM .......................................................................... 4 Floor cooling requirement................................................................................................................................................ 5
COOLING SOURCES ......................................................................................................... 9 Heat pump ......................................................................................................................................................................... 9 Tab water......................................................................................................................................................................... 10 Passive earth-water heat exchange ................................................................................................................................ 11
DISCUSSION .................................................................................................................... 12 CONCLUSION ................................................................................................................... 13 LITERATURE .................................................................................................................... 13 APPENDIX ........................................................................................................................ 15 A1. Water to water heat pump ...................................................................................................................................... 15 A2. Tab water.................................................................................................................................................................. 15 A3. Passive earth-water heat exchange ......................................................................................................................... 16
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Introduction Floor cooling is a potential method to reduce heat stress among pigs. The cooled floor allows the pigs to release more heat as conduction heat by contact with the floor surface. Floor cooling is suggested to be a preferable cooling method in housing facilities with existing floor heating, as the same pipes can be used for both heating and cooling. The cooling effect of a well-functioning floor cooling system is limited as floor temperature has to be maintained at a level where the pigs still find it attractive to rest on. Unfortunately, literature on suitable floor temperatures for finisher pigs is scarce. Geers et al. (1986) investigated finisher pigs’ preferences for cooled floor in comparison with increased air velocity under different ambient temperatures and found that pigs preferred increased velocity prior to areas with cooled floor. In their trial, the ambient temperature was between 14 and 25°C. Unfortunately, the exact floor temperatures were not specified. A project conducted at the experimental station Foulum in Denmark aimed to develop a fast reaction floor element that could remove heat up to 170 W m-2 (Larsen 2010; Strøm et al. 2010a; Strøm et al. 2010b). The investigation consisted of one trial in 2008 and one in autumn 2009. In the 2008 trial, they found no evidence that inlet water temperatures down to 10°C had a negative effect on the finisher pigs’ behaviour. In the 2009 trial, a sub-purpose was to determine the lower acceptable limit for floor temperature. This proved not to be possible, as the pigs refused to lie on the cooled floor at indoor temperatures above 26°C, without bedding. They estimated the maximum acceptable cooling capacity for pigs of 80 kg to be 170 W m-2 contact surface, and it was expected lower with smaller pigs. Further, they estimated that the acceptance of floor cooling was limited by the indoor temperature, meaning that pigs would avoid lying on the cooled floor, if the temperature difference between ambient air and floor surface was too large. They recommended no larger temperature intervals than caused by following combinations of ambient temperature and effect of floor cooling: 26.5°C and 160 W m-2 for 30 kg pigs, 25.1°C and 165 W m-2 for 60 kg pigs and 24.7°C and 170 W m-2 for 90 kg pigs (Larsen 2010). The purpose of this report was to assess •
how much heat it would be appropriate to remove by the floor cooling system,
•
which cooling source that will be most the cost effective strategy for cooling water led into the floor pipe system.
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The analysis assumed utilisation of the existing solid floor element (from Agrifarm) including the embedded heat pipes. Assessed cooling strategies were cold water provided from a water tap, a mechanical heat pump and a passive earth-water heat exchange system.
Effect of floor cooling system First step was to determine a relationship for how the cooling effect depended on the temperature difference between the water led through the floor and the room temperature. For a fast responding floor element placed in pens with finisher pigs, Strøm et al (2010b) found that if water temperature was equal to the room temperature, then the cooling effect was 47 W m-2 and that it increased by 4 W m-2 ºC if the water temperature was lower than the room temperature. The relatively large cooling effect that takes place even though the water has the same temperature as the room is because conduction heat from the pigs is released to the floor, resulting in a higher temperature than the room temperature. The heat transfer resistance from the floor surface to the water is probably lower in the floor used by Strøm et al (2010) than in the concrete floor element used by Agrifarm (Figure 1). Therefore, and in the absence of better measurement data, it was assumed that the cooling effect was 20% less in the floor used by Agrifarm than in the floor used by Strøm et al. (2010a). This results in cooling effects as a function of room temperature and water temperature, illustrated in figure 2.
Figure 1 Design of pipes for floor heating under solid floor in each pen
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Figure 2 Assumed cooling effect of Agrifarm’s floor element as function water temperature at three different room temperatures.
Floor cooling requirement A literature review (Hansen & Bjerg 2018) indicates that daily gain in finisher pigs begins to decrease when the temperature rises above 16 °C and that the feed efficiency begins decrease when the temperature rises above 23 °C. These values indicate that it is beneficial to begin the cooling when the temperature rises above 20 °C. Inspired by an approach suggested by Strøm et al. (2010b) the cooling requirements were calculated as the decline in the animal sensible heat release when the air temperature raise above 20 °C. The animal density on the cooled floor was assumed 0.45 HPU (Heat Production Units) corresponding to 1.8 100 kg pigs m-2. Figure 3 illustrates the consequent cooling requirement as a function of ambient temperature. The coloured curves are based on heat production formulas from CIGR 1984 and CIGR 2002. Data used for determination of the decline in sensible heat production at temperatures exceeding 20 °C is associated with significant uncertainties, and it is likely that the formulas used in CIGR 1984 overestimate the decline in sensible heat production at temperatures above 20 °C. Similarly is it likely that the formulas in CIGR 2002 underestimate the decline in sensible heat production at increased temperature in the temperature range from 20 to 30 °C, and therefore, a relationship based on the average of the two formulas are used in the further estimations.
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Figure 3 Cooling requirement as function of air temperature.
By combining the correlation found between water temperature and cooling effect in Figure 2 and the correlation between room temperature and cooling requirement in Figure 3, Figure 4 was developed. Figure 4 illustrates the water temperature that will result in the required cooling capacity as function of air temperature.
Figure 4 Water temperature to cause the required cooling capacity as function of room temperature
The relationship between pen temperature and outdoor temperature during summer periods recorded in an Agrifarm finisher pig unit (Hansen, 2016) was used in the determination of the yearly cooling requirement. Figure 5 shows this relationship for both hourly and daily values. To 6
eliminate the influence of ventilation control system, the graphs does not include recordings where the openings for the natural ventilation system were less than 85 percent open. It is shown that the recordings are scattered compared to the regression lines. For the hourly values an explanation is that the response in indoor temperature is delayed in relation to outdoor temperature. Further, a lot of the scattering in both hourly and daily observations can be explained by wind conditions.
Figure 5 The relationship between pen temperature and outdoor temperature during summer periods measured in an Agrifarm finisher pig unit (Hansen, 2016). Grey bullets illustrate hourly values and black bullets refer to daily values
The high heat capacity of the concrete floor (~60Wh °C-1 m-2 (
∙
/
)) causes a delay
when the inlet water temperature is used to control the floor surface temperature. Consequently, it will be impossible to control the floor surface temperature in relation to the hourly cooling requirement, and it occurs more realistic to control the inlet water temperature in relation to the expected average daily cooling requirement. Therefor was the correlation between outdoor and indoor temperature, shown in figure 5, used for determination of yearly cooling requirement.
Hourly values found by Møller & Lund (1995) were used to estimate the expected yearly number of days for each one-degree interval of average daily outdoor temperature (Figure 6).
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Figure 6 Number of days during a year for one-degree outdoor temperature intervals estimated from the Danish Reference Year (Møller & Lund, 1995)
The relationship between the required cooling effect and the outdoor temperature (Figure 7) was estimated by transforming the x-axis in Figure 3 by the correlation determined in figure 5.
120 y = 0.4x2 - 6.3941x + 9.0523 R² = 0.9999
Cooling effect , W m-2
100 80 60 40 20 0 12
14
16 18 20 22 Outdoor temperature, °C
24
26
Figure 7 Cooling requirement as function of outdoor temperature
The product of the number of days in each one-degree temperature interval and the belonging cooling requirement (estimated by the correlation mentioned in Figure 7) was used to determine a yearly cooling requirement of 30 KWh m-2.
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The relationship between outdoor temperature and water temperature (Figure 8) was utilised to assess to which extend the different cooling sources were capable of deliver the estimated cooling requirements. In the assessment, it was assumed that 10 l water h-1 m-2 was led through the floor, which required an inlet temperature corresponding to the blue curve in Figure 8. This temperature can be generated by mixing water from the cooling source with recirculated water from the floor, as long the water from the cooling source is colder or has the same temperature as indicated by the blue curve.
Figure 8 Water temperature causing the required cooling capacity as function of the outdoor temperature. Blue and red colours refers to inlet temperature and outlet temperatures, respectively. Dashed curve indicates average temperature
Cooling Sources Heat pump A heat pump used for cooling of the inlet water can either be designed as a water to air heat pump or a water to water heat pump, where a free cooling unit subsequently releases the heat to air, as illustrated in figure 9. The latter solution might be relevant to consider if the facility already includes a manure cooling system including a heat pump that in hot periods can be switched to cool the water used for the floor cooling system.
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According to Figure 7, a heat pump needs to deliver an cooling effect of ~60 W m-2 to fulfil the requirement up to outdoor temperature of up to 24°C. Assuming a power coefficient of 3.5 the yearly power consumption will be ~ 9 KWh m-2. The average energy cost for business customers in Denmark was 0.60 DKK/kWh in 2017 (Energistyrelsen 2017), corresponding to a yearly cost of ~5 DKK m-2.
Figure 9 Overview of system with a water to water heat pump
In addition to energy, there will be costs to depreciation, interest and maintenance, which for simplicity is estimated as a yearly cost of 10 % of the investment. A 5 kW water to air heat pump can deliver the required cooling for 20 pens corresponding to 80 m2 floor, and can be installed for approximately 55,000 DKK (Jensen 2018, personal communication), corresponding to a yearly cost of 70 DKK/m2. If an existing heat pump can be used, the investment includes a system to switch the heat pump´s cooling connection between the manure cooling circuit and the floor cooling circuit, as well as a free cooling units for releasing the heat to air. A 5 kW free cooling unit can be installed for approximately 9,000 DKK (Jensen 2018, personal communication), and assuming the total system can implemented for 15.000 DKK per 20 pens, then the yearly cost for depreciation, interest and maintenance will be 19 DKK m-2. In total, the yearly cost of this solution would be between 24 and 75 DKK m-2. Tab water Another strategy to ensure a cold water entry to the floor system, is by mixing cold tab water with the recirculating water, as illustrated in figure 10. From figure 8 it appears that a tab water 10
temperature of 10 °C can fulfil the cooling requirement up to an outdoor temperature of nearly 24 °C, and it is estimated that the yearly tap water consumption will be 1.6 m3 m-2 (see Appendix A2 for calculation). Business customers in Denmark pay ~ 4.5 DKK m-3 for water (Christensen 2018, personal communication) corresponding to a yearly cost for water to the floor cooling of ~ 7 DKK m-2.
Figure 10 Overview of system with a water tab water supply
Assuming an investment of 10,000 DKK per 20 pens the yearly cost for depreciation, interest and maintenance will be 13 DKK m-2. In total, the yearly cost of this system was therefore estimated to 20 DKK m-2. Passive earth-water heat exchange The last considered method for cooling of ingoing water is a passive earth-water heat exchange system, where the floor system is connected to subsoil tubes, from which heat from the circulated water is released to the soil. An illustration of the system is seen from figure 11. Based on a method suggest by Herez et al. (2017), appendix A3 includes an example of possible dimensioning of a tube system to deliver the required cold water. The investments is estimated to ~315.000 DKK for a system dimensioned to 20 pens corresponding to a yearly cost for depreciation, interest and maintenance of ~379 DKK m-2. To avoid an even more expensive solution it is assumed that the inlet water is 15 °C, which, according Figure 8, is sufficient to meet the requirements as long as the outdoor temperature does not exceed 22 °C. As a consequence there might be a few days each year where this system is unable deliver the entire requirement.
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Figure 11 Overview of system with a passive earth-water heat exchanger
Discussion Literature has shown difficulties in specifying a threshold for when the floor surface is too cold. Literature indicates that the willingness to lie on the cooled floor depends on the temperature of the ambient air. There are indications that pigs prefer colder floor at high ambient temperature (Shormann & Hoy 2006). But also that the ambient temperature can be too high for the pigs to choose the cooled floor, because they would experience a kind of shock to the cold if the temperature difference between floor surface and ambient air exceeds a certain limit (Larsen 2010). The concerned study included an experimental floor with a very low heat capacity and heat resistance which expectedly reduced the floor surface temperature significantly compared with a concrete floor at the same water temperature. The exact limit is not known, however experiences have shown no negative effect on the behaviour of finisher pigs, when the ingoing water in the floor cooling system was 10°C and the ambient air was 28°C (Strøm et al. 2010). Conditions for heat release at high temperatures are generally better for pigs lying on slatted or drained floor than for pigs lying on solid floor. This increases the importance of improvement of the conditions for heat release for pigs on the solid floor. With this perspective it becomes less critical that the suggested system supports only the pen area with solid floor, meaning that only two fifth of the pigs will gain from the cooling system at a time. A limitation of the applied Agrifarm floor element is that the large heat capacity makes it impossible to control the floor temperature to follow the diurnal variations in the cooling requirement. On the other hand, the large heat capacity may prevent overcooling of the floor, making the solid floor unattractive for the pigs to lie on. A way to control the temperature of the ingoing water to the system, is to base the system on the online weather forecast from day to day. 12
Further studies are relevant to determine the optimal solution for use of the weather forecast to set the required inlet water temperature. Three methods for cooling of the circulating water were considered. It was found that both heat pumps and tab water could deliver the required cooling, whereas the needs could not be fulfilled entirely by a passive earth-water heat exchange system. Generally the costs related to the investment (depreciation, interest and maintenance) was high in comparison with the cost for energy or water consumption. Especially, the passive earth-water heat exchange system required an investment of a size where it became unattractive from an economical point of view. The lowest total cost appeared for the tap water method. However, the large water consumption does not comply with the Agrifarm concept of a facility with a low environmental footprint. If water could be stored and reused for other, existing purposes the cost for the water consumption could be reduced and the ethical discussion of water consumption would be changed.
Conclusion In conclusion, 60 W m-2 would be an appropriate heat removal effect of the floor cooling system, under Danish outdoor conditions. It cannot be concluded whether this cooling effect would influence the pigs’ perception of the solid floor, as a desirable spot in the pen, but based on previous literature, the cooling effect is not expected to cause a negative perception of the solid floor. The tab water solution occurs as the most cost effective source for floor cooling and the required system can easily be implemented in the Agrifarm finisher unit.
Literature Energistyrelsen, 2017. Cited February 2018, available online: https://ens.dk/ansvarsomraader/energi-klimapolitik/erhvervslivets-energiforhold/fakta-om-elprisererhverv-og Christensen, M. G. (2018) personal communication. Michael Groes Christensen, Senior consultant, Economist, SEGES. Phone: +45 3339 4333, e-mail:
[email protected] CIGR (1984) Report of working group on climatization of animal houses. Commission Internationale du Génie Rural CIGR (2002) Report of working group on climatization of animal houses – Heat and moisture production at animal and house levels. Commission Internationale du Génie Rural
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Geers, R., Goedseels, V., Parduyns, G. & Vercruysse, G. (1986) The group postural behavior of growing pigs in relation to air velocity, air and floor temperature. Applied Animal Behaviour Science, 16:353-362 Hansen. R. K. & Bjerg, B. S. (2018) Optimal ambient temperature with regard to feed efficiency and daily gain of finisher pigs. In preparation for the EurAgEng 2018 Conference. Herez, A., Khaled, M., Murr, R., Haddad, A., Elhage, H. & Ramadan, M. (2017) Using geothermal energy for cooling – parametric study. Energy Procedia, 199:783-791 Hviid, J. (2013) Priskalkulation 2013 vedrørende landbrugsbyggeri. Videncentret for Landbrug ved konsulent Jørgen Hviid Jensen, S. (2018) Personal communication. Søren Jensen, Sales Manager, Klimadan. Phone: +45 9627 7070, e-mail:
[email protected] Larsen, H. (2010) Modulært gulvelement til køling og opvarmning i smågrise- og slagtesvinestalde. Delrapport 6. Model og program til styring af fremløbstemperatur til gulvelementer. Møller, J. M. & Lund, H. (1995) Design reference year, DRY. Meddelelse nr. 281. Laboratoriet for varmeisolering. Danmarks tekniske universitet. P. Lindeberg (2018). PEL-slanger. Cited March 2018, available online: https://www.plindberg.dk/detaljer/pel-slanger Schormann, R. & Hoy, S. (2006) Effects of room and nest temperature on the preferred lying place of piglets – a brief note. Applied Animal Behaviour Science, 101:369-374 Strøm, J. S., Kai, P. & Kristiansen, J, K. (2010a) Modulært gulvelement til køling og opvarmning i smågrise- og slagtesvinestalde. Delrapport 3. Termisk karakterisering af gulvelement i slagtesvinestald. Intern rapport. Husdyrbrug nr 25. http://web.agrsci.dk/djfpublikation/djfpdf/Ir_25_husdyrbrug_50756_rapport.pdf Assessed March 16 2016. Strøm, J. S., Zhang, Q. & Kai, P. (2010b) Modulært gulvelement til køling og opvarmning i smågrise- og slagtesvinestalde. Delrapport 4. Strategi for styring af fremløbstemperatur til kølet gulvelement i slagtesvinestald. Sørensen, T. L., Friis-Nielsen, M. B., Jørgensen, M. & Riis, M. L. (2010) Temperering af ventilationsluften i en farestald med et jordkølevarmeanlæg. Meddelelse nr. 866. Videncenter for svineproduktion
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Appendix A1. Water to water heat pump The yearly cooling requirement, determined from figure 6 and 7, was calculated as it appears in table A1. With this basis and a COP value of 3.5, the yearly energy consumption per m2 was calculated. Table A1 Cooling requirement and energy consumption of water to water heat pump
Cooling Energy Average Cooling requirement consumption, Energy Number of days requirement per per year, diurnal W/m^2 of consumption, temperature a year day, W/m^2 W/m^2 heat pump kWh 24 1 85.99 85.99 24.57 0.59 23 0 73.59 0.00 0.00 0.00 22 0 61.98 0.00 0.00 0.00 21 3 51.18 153.53 43.87 1.05 20 5 41.17 205.85 58.81 1.41 19 10 31.96 319.64 91.33 2.19 18 5 23.56 117.79 33.66 0.81 17 8 15.95 127.62 36.46 0.88 16 21 9.15 192.08 54.88 1.32 15 16 3.14 50.25 14.36 0.34 Total year 1252.76 357.93 8.59
A2. Tab water Inlet and outlet water temperature were determined from the correlations with outdoor temperature, shown in figure 8. The share of tab water needed, corresponding to the average diurnal temperature, was then calculated from equation A2.
=
∗
! "
+ $1 − ' ∗ (
"
(A2)
Results are seen in table A2. Table A2 Tab water consumption for floor cooling
Average Number Share of Tab water Tab water diurnal of days a Inlet Outlet Tab water tab consumption. consumption temperature year temperature temperature temperature water l/m^2/day l/m^2/year 24 1 8.81 16.19 10 1.00 240.00 240.00 23 0 12.56 18.88 10 0.71 170.73 0.00 22 0 16.02 21.34 10 0.47 112.62 0.00
15
21 20 19 18 17 16 15
3 5 10 5 8 21 16
19.17 22.02 24.57 26.82 28.77 30.42 31.77
23.56 25.56 27.32 28.85 30.14 31.21 32.04
10 10 10 10 10 10 10
0.32 0.23 0.16 0.11 0.07 0.04 0.01
77.73 54.53 38.04 25.77 16.34 8.91 2.96
233.19 272.63 380.37 128.84 130.69 187.09 47.39
A3. Passive earth-water heat exchange To calculate the required pipe length of the geothermal heat exchange system, a combination of equation A3.1 and A3.3 was applied. The calculation of required length originates from Herez et al. (2017), who assessed a similar issue with a geothermal heat exchange system with circulating water. Equation A3.1 to A3.12 originates from Herez et al. (2017). The heat transfer rate, Q (W), can be calculated either from equation A3.1 or equation A3.3. )=
∗ *+ ∗ ∆ (A3.1)
Where ΔT is the temperature difference between ingoing and outgoing water (°C), Cp is the specific heat of water (kg/s) and m is the mass flow rate of water (kg/s), which is calculated from = - ∗ Ṽ (A3.2) With ρ being the density of water (kg/m3) and Ṽ being the volumetric flow rate (m3/s). )=
∆
/0
12
(A3.3)
Where Rt is the total heat transfer resistance (K/W) and ΔTlog is the logarithmic mean temperature difference, calculated from equation 14 ∆
/0
=
3
0
−
4−3 5− 0− ln 8 − 9 5
4
(A3.4)
With To being the temperature of the outgoing water (°C), Tg being the temperature of the ground (°C) and Ti being the temperature of the ingoing water (°C). And where Rt is calculated from equation 15
16
12 = 1:0; + 1:0;?,+ + 1:0;?, (A3.5) With Rconv,w being the convective heat transfer resistance (K/W), Rcond,p being the conductive heat transfer resistance of the pipe (K/W) and Rcond,s being the conductive heat transfer resistance of the soil (K/W). The heat transfer resistances are calculated from 1:0; =
1 ℎ ∗ $2 ∗ B ∗
5
∗ C' (A3.6)
With ri being the inner radius of the pipe, L being the length of the pipe (m) and h being the convective heat transfer coefficient (W/m2 K), which is calculated from ℎ=
D ∗E F (A3.7)
With k being the thermal conductivity (W/m K), D being the inner diameter of the pipe (m) and Nu being the Nusselt number, calculated from D = 0.023 ∗ 1
.J
∗ KL; (A3.8)
Where Pr is the Prandtl number and Re is Reynolds number, which can be calculated from Ṽ -∗M∗F -∗O∗F 1 = = N N (A3.9) With v being the velocity (m/s), A being the cross section area of the pipe (m2) and μ being the dynamic viscosity of water (kg/m s). 1:0;?,+ =
ln P 0 Q 5
2∗B∗E∗C
(A3.10)
Where ro is the outer radius of the pipe. 1:0;? =
1 1 = R 2∗B∗C 8∗T ln B ∗ F (A3.11)
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With S being the conductive shape factor and Z being the depth of the pipe in the ground (m).
To calculate the required pipe length needed to cool the water for the floor cooling system, the two equations for Q were put equate (Equation 18). From this new equation, the pipe length was calculated. For this purpose the parameters and equations were added to an Excel sheet and the “What if – Goal Seeking” analysis was applied. ∗ *+ ∗ ∆ =
∆
/0
12
(A3.12)
When the length was determined, the cost of implementation was calculated for a system consisting of recirculating water in a PVC tube system in a depth of 2 m. The applied parameters and required dimensions of the pipe system, corresponding to a floor cooling system for 20 pens, or 83.2 m2 solid floor with a flow rate of 10 l/m2/h, are seen from table A3.1. Due to a known achievable cooling capacity of the system, the outlet temperature of the earth-cooled water was set to 15°C (Sørensen et al. 2010). The corresponding costs are seen from table A3.2.
Table A1.1 Pipe length and applied parameters in determination of the required length
Parameter Volumentric flow rate, Ṽ v Density of water, p Inner diameter, D Outer diameter, Do Dynamic viscosity of water, μ Cross section area of the pipe, A Reynolds number, Re Prandtl number, Pr n Nusselt number Thermal conductivity of pipe material, k convective heat transfer coefficient, h Outlet temperature, To Inlet temperature, Ti Ground temperature, Tg Logarithmic mean temperature difference, ΔTlog Pipe length, L Pipe depth, z Resistance, conduction in the pipe, Rcond,p
Value 0.000231111 0.766370936 995.7 0.0196 0.02 0.00076 0.000301566 19679.31658 5.43 0.3 104.0820397 0.5 2655.154075 15 20.5975 12.8 4.423691895 1094.765197 2 5.87704E-06
Unit m^3/sec m/s Kg/m3 m m kg/m s m2
W/m K W/m^2 K °C °C °C m m K/w
18
Resistance, conduction in the soil Rcond,s Resistance, convection in the water Rconv,w Total resistance, Rt Rate of heat exchange, Q = Δtlog/Rt Mass flow rate of water, m Specific heat of water, Cp Temperature difference between inlet and outlet water, ΔT Q = m*Cp*ΔT, kW Q = m*Cp*ΔT, W
0.000808799 5.58989E-06 0.000820266 5393 0.230117333 4.187 5.5975 5.393198385 5393.198385
K/w K/w K/w W kg/s kJ/kg K °C kW W
Table A3.2 Cost of a passive earth-water heat exchange system
Parameter Labor and machinery 1 m in depth 1 m Labor and machinery 1 m in depth 2 m 100 meter PEL-tube, diameter 20 mm 1 meter PEL-tube, diameter 20 mm Circulation pump Cost per system (83 m^2 solid floor) Cost per m^2 Cost per year (10 % of investment)
Cost Currency 142 DKK 284 DKK 280 2.8 1120 315,099 3,787 379
DKK DKK DKK DKK DKK DKK
Source Hviid 2013 Guestimate P. Lindberg 2018 Hviid 2013
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