REHAU MONTANA ECOSMART HOUSE PROJECT Bozeman, MT RMEH 04 Test Report

Transcription

1 REHAU MONTANA ECOSMART HOUSE PROJECT Bozeman, MT RMEH 04 Test Report Evaluation of Pickup Response Time of Radiant Floor Using Different Water Supply Temperatures F. Javier Alvarez, LEED GA Kevin Amende, P.E. Mechanical and Industrial Engineering Department Montana State University 07/08/2015

2 Introduction The REHAU MONTANA ecosmart house is a residential construction and research project sponsored by REHAU, an international manufacturer of polymer-based innovations and systems, including sustainable building solutions. This project aims to expand the industry's body of knowledge regarding environmental and human sustainability. The home is designed for three generations living together the homeowners, their daughter, and the homeowners parents. The house accommodates a family member who uses a wheelchair, with design features that include: No-step entries, 36 in. wide doorways with no thresholds, hand-held shower heads and grab bars, lever handles on all doors and plumbing fixtures, accessible light switches, tambour doors for ease of access to cabinets, smooth floor surfaces (wood, ceramic tile and stained concrete) and an elevator. A goal of the REHAU MONTANA ecosmart house is to achieve near net-zero status by combining a tight building envelope with efficient heating and cooling systems. To achieve this, the house includes technologies such as insulated concrete forms, structural insulated panels, high-performance upvc (vinyl) window and door systems, thermal solar panels, a geothermal heat pump system that produces warm or chilled water depending upon the season, radiant floor heating and cooling to distribute that energy, radiant ceiling cooling panels, a ground-air heat exchanger for fresh air, a snow and ice melting system and PEX plumbing. The house also includes redundant mechanical systems such as a hydronic boiler and ductwork for forced-air heating and cooling. Since construction was completed at the end of 2012, the house has been recognized with Energy Star and LEED certifications, has achieved an excellent HERS index score of 32, and has received the Green Builder Magazine Green Home of the Year award among others. A major objective of the research is to determine how the various building systems are best integrated to optimize energy consumption, comfort and life-cycle costs. More than 300 sensors are positioned throughout the house to collect data during the research phase. The mechanical systems are controlled remotely through the REHAU Smart Control system. Starting in April 2013, a team of researchers from Montana State University collected, interpreted and evaluated data generated by the various systems as they would be used in an everyday life situation to determine how they contribute to energy efficiency. Through a series of nine research tests, the efficiency of the REHAU hydronic mechanical systems was evaluated to measure and compare the efficiency, comfort and responsiveness of these systems with traditional mechanical HVAC systems. This test report provides the data and findings of one of those research tests. For 18 months, the house was vacant to allow researchers full access, and without occupants to consume energy or interfere with experiments. During this period, many tours of the house were given to demonstrate its systems to mechanical contractors, builders, architects and engineers. Thanks to the Hoy family for their inspiration, patience, and cooperation with REHAU and the MSU research team during this extensive project. Additional information about REHAU Montana ecosmart house can be found at: Jul 08, 2015 Page 1

3 Executive Summary Hydronic radiant floor heating (RFH) systems work by circulating warm fluid through a network of PEX pipes embedded in the floor. There are many ways to install these PEX pipes, including poured wet thermal mass systems such as structural concrete or gypsum cement overpours, and dry systems using aluminum heat transfer panels and plates. The material placed around the heating pipes is referred to as the thermal mass since the material conducts heat from the pipes and transfers it to the heated space. Each of these installation types has advantages and disadvantages for a given project. Some factors which influence the installation type include: Is the heated floor on-grade or suspended? Which installation type is most cost-effective? Is the desired thermal mass material available locally? Can the building design accommodate the weight of an overpour? Will the floor be used solely for heating, or as a heating and cooling surface? Is an overpour being used already for other construction reasons, such as a noise/fire barrier? Is the building located in a region that experiences wide temperature swings over time? Does the building design accommodate the height of the thermal mass overpour? What strategy for control of the heating system is to be used? What response time for the heated floors is expected? REHAU Montana Ecosmart House (RMEH) in Bozeman is a LEED certified house with high levels of insulation and low heat loss, resulting in a HERS index score of 32. Walls on the first two levels were built using insulated concrete forms (ICF) with 8 inches of concrete, increasing the overall thermal mass of the house. Radiant floor heating was installed throughout the house using ½ PEX tubing installed via 3 techniques, from the ground floor to top floor: i. Ground level: Within the 4 inch poured concrete floor on-grade ii. Main level: Within a 3 inch suspended concrete floor iii. Top level: Within a 1 ½ inch overpour of GYP-CRETE gypsum cement These installation types were selected due to: i. The ground level slab was constructed on-grade using Portland cement concrete, including insulation below the floor; the concrete was an obvious location for the heating pipes ii. An Amvic AmDeck insulated concrete form was selected for the main level of the house; this system includes a 3 inch PC concrete pour, an obvious location for the heating pipes iii. With plans to operate the radiant floors also for cooling, aluminum panels were not an option for the top level, due to the possibility of condensation on the panels in cooling mode. The framing and the structural subfloor accommodated the height and weight of the overpour. Radiant floor heating was installed with ½ PEX tubing using tube layout patterns and spacing described in Appendix D. Depending on the room, tube spacing ranged from 6 on-center to 9 on-center, with circuit lengths ranging from 106 (in an interior bathroom) to 357 (in the ground floor rec room). REHAU PRO- BALANCE balancing manifolds were adjusted so that each circuit had the correct flow rate, based on calculated heat loss of each room. Experiment RMEH04 was conducted at the house to measure the pickup (response) time of the radiant floor heating systems from cold start using Heating Water Supply (HWS) temperatures of 105 F and 120 F, in two scenarios. The experiment compared the response time of the three floor installation types, Jul 08, 2015 Page 2

4 as well as how the room air temperature followed the floor temperatures. Each experiment started at 60 F floor/room temperature and heated floors up to 90 F over several days, when possible*. *Both of these temperatures are extreme: For a residence, 60 F set-back temperature is lower than typical, and 90 F floor temperature is much hotter than normal. This data could be used to evaluate the suitability of setting back room temperatures during unoccupied periods, a scheme that is generally not employed with poured thermal mass radiant heating systems due to concerns about slow response time. Most living spaces with radiant floor heating run at 68 F room temperature, measured at the thermostat. Area weighted average response times of the floors for each level, with two HWS temperatures, are summarized in Table 1. The table also shows time differences. While there are various ways to analyze this data, one comparison looks at the total overall pickup times of the floor at each level for a specific temperature pick-up range, using a specific HWS, to compare the effect of thermal mass thickness. For instance, when heating floors from 62 F to 68 F: i. The ground level floor took 3.1 hours to reach 68 F from 62 F when the HWS temperature was 120 F. ii. Surprisingly, the main level floor took 4.5 hours to reach 68 F from 62 F when the HWS temperature was 120 F, or 45% slower than the ground level. iii. The upper level floor took approximately 2.8 hours to reach 68 F from 62 F when the HWS temperature was 120 F, or 10% faster than the ground level. Data also shows that it took approximately 50% less time to increase the floor temperatures from 60 F to 90 F with a 120 F HWS compared to 105 F HWS. The supply water temperature has a significant impact on floor response time. While heating system designers can use this data to make decisions about control strategies and temperature set-back, even a small set-back of 4 F (64 F to 68 F) for a relatively thin 1 ½ overpour can still take almost 2.5 hours to recover using a low HWS of 105 F, or 2 hours to recover using a high HWS of 120 F. Note: In these experiments, measured room air temperatures followed floor temperatures quite closely. This relationship may not be typical in other houses, with various construction types and levels of airtightness. Experiment Description The purpose of this experiment was to measure the pickup response time of radiant floor heating (RFH) from 60 F to 90 F using a boiler (see Appendix B. Experiment Notes, for details) to supply water temperatures of 105 F and 120 F. Starting at 60 F, floor temperatures were raised as quickly as possible and the pickup time was measured at 2 F increments. Simultaneously, the maximum achievable air temperature was determined. Finally, a comparison between the three different floor configurations was conducted. Fixed temperatures of 105 F and 120 F were set on the mixing valve (see figure in cover page) to ensure consistent radiant zone supply temperatures. The corresponding buffer tank temperatures were set at 115 F and 130 F with a dead band of 8 F below setpoint. The REHAU Smart Controls (RSC) Jul 08, 2015 Page 3

5 controlled the radiant supply temperature for each zone. The 105 F experiment was performed over a 3- day period while the 120 F experiment was performed over 2½-days. The hydronic radiant floor is made of 1/2 Cross-linked Polyethylene (PEXa) pipe. The three different types of floors in the house are as follows: i. Basement: Insulated 4 slab on grade, uncovered (no flooring) ii. Main floor: 12 Expanded Polystyrene (EPS) blocks deck on 1-5/8 x10 metal joist 16 OC with an over poured 3 reinforced concrete topping slab, finished with a hardwood panel. iii. Upper floor: 1.5 GYP-CRETE over pour on a wooden joist structure, finished with a hardwood panel. Results Pickup Time Area weighted average pickup times for each level and hot water supply (HWS) temperature are shown in Table 1. Table 1. Pickup Times for Each Floor Based on HWS Temperature Lower Level (Slab) Main Level (Amvic) Upper Level (Overpour) Pickup Pickup Time (hrs) Pickup Time (hrs) Pickup Time (hrs) Interval 105 F 120 F Time % 105 F 120 F Time % 105 F 120 F Time % ( F) HWS HWS Delta Delta HWS HWS Delta Delta HWS HWS Delta Delta 60 to % % % 62 to % % % 64 to % % % 66 to % % % 68 to % % % 70 to % % % 72 to % % % 74 to % % % 76 to % % % 78 to % % % 80 to % % % 82 to % % % 84 to % % 86 to % % 88 to % % Total Time Average per Two % % % Degrees F Notes: Lower level never achieved 90 F during the 105 F HWS configuration so average for this column was computed from 60 to 82 F only Time Delta and % Delta columns refer to the decrease of 120 F values with respect to 105 F ones As expected, the pickup time increased as floor temperatures increased due to the decrease in temperature differential between the slab and HWS temperature. During the 105 F HWS scenario it was Jul 08, 2015 Page 4

6 observed that the lower level slab was not able to achieve the desired 90 F within the specified 3-day experiment. The lower level slab had a peak temperature of 84 F during this timeframe. Figure 1 and Figure 2 show the space and slab temperatures versus time for the lower level of the RMEH during the two test scenarios. The slab temperature is expected to slowly approach an upper limit somewhere below the HWS temperature setpoint based on how steady the heat transfer rate is in the RMEH. During this experiment it was determined that the required overall pickup time needed to increase the floor temperatures from 60 F 90 F was 51% less for a 120 F HWS when compared to a 105 F HWS. Figure 1. Lower Level Air and Floor Temperatures vs. Time Using 105 F HWS Figure 2. Lower Level Air and Floor Temperatures vs. Time Using 120 F HWS Jul 08, 2015 Page 5

7 The main level floor, constructed with Amvic AmDeck insulated concrete forms, took 65.7 hours to reach 90 F with a 105 F HWS. In contrast, the upper level constructed with a GYP-CRETE overpour reached 90 F in as little as 17.8 hours from a 60 F initial temperature. Figure 3 and Figure 4 show the average floor and air temperatures for the main level of the RMEH. Near the end of the experiment the floor and air temperatures began to stabilize due to the limits put in place to prevent the slabs from overheating. RSC was configured this way to avoid structural and floor material stress that could occur from excessive floor temperatures. Figure 3. Main Level Air and Floor Temperatures vs. Time Using 105 F HWS Figure 4. Main Level Air and Floor Temperatures vs. Time Using 120 F HWS Jul 08, 2015 Page 6

8 Air temperatures were consistently much closer to floor temperatures during the 105 F HWS experiment. During the 120 F HWS experiment, differences up to 5 F were observed between air and floor temperatures. The upper level floor constructed with 1.5 gypsum concrete overpour, took 32.7 and 17.8 hours to reach 90 F from 60 F with 105 F and 120 F HWS respectively. Figure 5 and Figure 6 show the average floor and air temperatures for the upper level of the RMEH. Figure 5. Upper Level Air and Floor Temperatures vs. Time Using 105 F HWS Figure 6. Upper Level Air and Floor Temperatures vs. Time Using 120 F HWS Jul 08, 2015 Page 7

9 Maximum Achievable Air Temperature Air and floor temperatures for each level were calculated based on an area-weighted average. These values are listed in Table 2. Air temperatures were recorded when the floor temperatures initially hit 90 F and at the end of the experiment. These results provide perspective regarding maximum air temperatures achievable when a floor initially reaches temperature and when it stabilizes at setpoint. Floor temperature limits set within the RSC were accounted for in analysis of this experiment. The cumulative average temperature for the RMEH at the end of the experiment was very close to 90 F for both HWS temperature scenarios. These finding coincide with observations to be expected in radiant floor systems when they achieve near steady-state conditions. Table 2. Estimation of the Maximum Air Temperature Achievable Simultaneously at the RMEH Zone (1) Floor Area (ft 2 ) Area Ratio Initial Air Temp When Floor Reached 90 F ( F) (2) Max Air Temp at End of Experiment ( F) (3) 105 F HWS 120 F HWS 105 F HWS 120 F HWS Rad Zone LL1RAD- Meeting Room Rad Zone LL3RAD- Studio / Bathroom Rad Zone LL6RAD - Storage Rad Zone ML1RAD - Front Entry and Half Bath Rad Zone ML3RAD- Study Rad Zone ML4RAD - Dining and Living Rooms Rad Zone ML5RAD - Kitchen Rad Zone ML6RAD - Laundry Rad Zone UL1RAD - Master Bedroom Rad Zone UL2RAD - Master Bath Rad Zone UL3RAD - Daughters Living Area Rad Zone UL4RAD - Daughters Bed Room Rad Zone UL5RAD - Guest Bedroom and Bath Rad Zone UL6RAD - Daughters Bath Rad Zone UL7RAD - Hallway Total / Weighted Average Notes: (1) LL = Lower Level; ML = Main level; UL = Upper level (2) Maximum temperature achieved when floor did not reach 90 F (3) Floor temperature limit was set to 95 F and 90 F, respectively using RSC Fluid Temperature A plot of the radiant supply and return fluid temperatures versus time illustrates the evolution of the average temperature difference (ΔT) for each buffer tank setpoint as seen in Figure 7 and Figure 8. These plots also show that it took approximately 36 hours to effectively reach setpoint temperature in the buffer tank for both the 115 F and 130 F setpoints. The buffer tank achieved average temperatures of 104 F and 120 F after the initial 36 hour ramp up time. These averages are below setpoint by almost 10 F. Even Jul 08, 2015 Page 8

10 though the buffer tank deadband was set at 8 F in the RSC, the average temperatures were expected to be no more than 4 F less than setpoint. These plots also show how the boiler needed approximately 36 hours to bring the buffer tank to its setpoint temperature while under heavy load from the radiant zones. Figure 7. RFH Supply, Return, and Buffer Tank Temperature at 105 F HWS Setpoint Figure 8. RFH Supply, Return, and Buffer Tank Temperature at 120 F HWS Setpoint Jul 08, 2015 Page 9

11 Temperature change between the HWS and HWR versus time was also explored (Figure 9). During the initial startup of the experiment, large temperature differences were observed as the boiler was trying to bring the buffer tank to setpoint. This was expected since the RMEH was cold at startup and the heat exchange rate between the floor and air was at its peak. As each test scenario approached steady state, temperature changes of approximately 12 F and 18 F were calculated for HWS setpoints of 105 F and 120 F, respectively. Figure 9. Temperature Change between HWS and HWR vs. Time Jul 08, 2015 Page 10

12 Appendix A. Test Schedule Sheet Jul 08, 2015 Page 11

13 Appendix B. Experiment Notes Data for experiment RMEH was collected during the following dates: Scenario F Water Supply Temperature: 4/17/2014 4/20/2014 Scenario F Water Supply Temperature: 4/24/2014 4/27/2014 Boiler Data The boiler used in this experiment is a Triangle Tube Prestige Solo 175. This is a condensing high efficiency low NOx gas-fired boiler with modulating input from MBH, 96% efficiency (AFUE) and up to 154 MBH heating capacity (DOE). Fuel available at the RMEH is natural gas. Figure 10. Condensing Boiler at the Mechanical Room of the RMEH Jul 08, 2015 Page 12

14 Appendix C. Data Collection Parameters RSC and National Instruments (NI) data acquisition systems were used to collect data for this experiment. Data was collected for the following points: RSC Data Points Outdoor Air Temperature Zone Setpoint Temperature Zone Actual Temperature Slab Sensor Temperature Slab Set Point Temperature Boiler HWS/HWR Temperature RFH HWS/HWR Temperature Buffer Tank Temperature NI Data Points Gas Consumption from Boiler Jul 08, 2015 Page 13

15 Appendix D. Radiant Floor Piping Design Jul 08, 2015 Page 14

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19 Appendix E. Picture of House during and after Construction Figure 11. Phase of construction of the ground floor showing the finished gravel layer Figure 12. Slab-on-grade floor with 4 inch concrete over 2 inch rigid board insulation on ground level Jul 08, 2015 Page 18

20 Figure 13. Construction of the main level floor showing the AMVIC AmDeck structure Figure 14. ½ PEX pipe layout on top the main level AMVIC AmDeck structure Jul 08, 2015 Page 19

21 Figure 15. Main floor with 3 inch concrete surrounding ½ PEX pipes over insulated AmDeck system Figure 16. View of the finished concrete slab on the main floor Jul 08, 2015 Page 20

22 Figure 17. Top floor with 1 ½ inch gypsum cement overpour surrounding ½ PEX pipes over wood floor (before the overpour) Figure 18. Top floor with 1 ½ inch gypsum cement overpour surrounding ½ PEX pipes over wood floor (after the overpour) Jul 08, 2015 Page 21

23 Appendix F. References 1. REHAU Unlimited Polymer Solutions (2013, May). REHAU Radiant Heating Systems. Design Guide. Retrieved from 2. REHAU Unlimited Polymer Solutions (2013, January). Sustainable Building Technology. Indoor Comfort Solutions for High-Performance Buildings. Retrieved from 3. AMVIC Building System (2007). AMDECK Technical & Installation Manual. Retrieved from 4. MAXXON (2015). Gyp-Crete Data Sheet. Retrieved from Jul 08, 2015 Page 22