Radiant Slab Research Articles

Signature analysis calibration of a school energy model using hourly data

An EnergyPlus model of a school with displacement ventilation and radiant slab thermal control was calibrated using signature analysis. Capacity to model these technologies is relatively recent in simulation software, and little has been published on calibration of energy models with these systems. The calibration of the as-built model required eleven adjustment iterations. Between iteration one and three; a group of weather-independent factors were modified. Between iterations four and eight; weather-dependent parameters were updated. The last three iterations addressed weather-independent electric demand parameters, for which hourly data were used. The calibrated model complied with the mean bias error (MBE) and coefficient of variation (CV) requirements of ASHRAE Standard 14. Hourly data were key to meeting the criteria for an adequate match between simulation estimates and the measured data. The MBE and CV of root-mean-squared error were 0.5% and 7% for electricity with daily data and 5% and 9% for gas with weekly data.

Field analysis of indoor air quality in high rise and low rise green offices with radiant slab cooling systems in Malaysia

Even though the green building concept is fairly new in Malaysia, the development of this industry has been growing in recent years prior to the launch of Malaysia’s own standard, namely the Green Building Index (GBI). One of the criteria assessed in the GBI is the energy efficiency, which takes about 21% of the overall assessment. Considering this, the passive design has been included in the green building concept to reduce the energy usage without compromising occupant thermal comfort. This study attempts to assess the passive design effectiveness in terms of indoor air quality in green office buildings in the tropics. Two green office buildings that incorporated the radiant slab cooling and conventional cooling system have been selected as case studies. A detailed assessment in terms of thermal comfort parameters (temperature and relative humidity), indoor pollutants’ concentration (carbon dioxide, carbon monoxide and formaldehyde) and air movement was carried out. The results showed that the thermal comfort parameters fall within the Malaysian Standard (MS1525:2007) and ASHRAE Standard-55 2010 except for the air movement in both buildings. Based on the results obtained, future buildings using the radiant slab cooling can have a better comfort level from the lesson learned from both buildings.

Modeling a radiant floor system with Phase Change Material (PCM) integrated into a building simulation tool: Analysis of a case study of a floor heating system coupled to a heat pump

This work describes a model developed to simulate a radiant floor system with PCM in simple building types. The building simulation model has been validated by comparing its behavior with Energy Plus. The PCM radiant floor model is based on a one-dimensional finite difference scheme where the effective capacity method is used for PCM simulation. Some adjustments have been made to this one-dimensional scheme so that the thermal effect of two-dimensional heat transfer within the radiant floor slab is taken into account.The results of an analyzed case study are also presented in this paper. Here, the PCM floor heating system is fed by a heat pump which mainly operates during night time, thus reducing the costs of electric energy consumption.

Performance analysis of an integrated UFAD and radiant hydronic slab system

In this paper, an EnergyPlus model was used to simulate the operation of a novel integrated HVAC system. This system combines an underfloor air distribution system with a cooled radiant ceiling slab. A cooling tower supplies water to pre-cool the structural slabs during the night and early morning period. The paper compares the performance of this system to both a typical overhead system and a typical UFAD system in the cooling season for the Sacramento, California climate. When compared to the overhead system, the integrated UFAD/Radiant system shows a 22–23% reduction in total energy consumption during the peak cooling months (June to August) and a 31% reduction in peak hourly electricity demand. When compared to the UFAD system, these reductions are 21–22% and 24% respectively. An investigation of the simulation results showed that the integrated UFAD/Radiant system also improves occupant thermal comfort and reduces thermal decay issues in the underfloor plenum.

Control characteristics and heating performance analysis of automatic thermostatic valves for radiant slab heating system in residential apartments

Computer simulations and experiments are carried out to research the control characteristics and heating performances for a radiant slab heating system with automatic thermostatic valves in residential apartments. An electrical equivalent R–C circuit is applied to analyze the unsteady heat transfer in the house. In addition, the radiant heat transfer between slabs, ceilings and walls in the room is evaluated by enclosure analysis method. Results of heating performance and control characteristics were determined from control methods such as automatic thermostatic valves, room air temperature-sensing method, water-temperature-sensing method, proportional control method, and On–Off control method.

Energy performance optimization of radiant slab cooling using building simulation and field measurements

Few field studies of energy performance of radiant cooling systems have been undertaken. A recently constructed 17,500 m 2 building with a multi-floor radiant slab cooling system in the tower was investigated through simulation calibrated with measured building energy use and meteorological data. For the very cold, dry region where the building was located, it was found that a typical floor of the tower would have had 30% lower annual energy use with a conventional variable air volume system than with the as-built radiant cooling-variable air volume combination. This was due to (1) simultaneous heating and cooling by the existing radiant cooling and air systems, (2) the large amount of free cooling possible in this climate, and (3) suboptimal control settings. If these issues were remedied and combined with improved envelope and a dedicated outdoor air system with exhaust air heat recovery, a typical floor could achieve annual energy use 80% lower than a typical floor of the existing building HVAC system. This shows that radiant thermal control can make a significant contribution to energy-efficiency, but only if the building design and operating practices complement the strengths of the radiant system.

A field study of occupant thermal comfort and thermal environments with radiant slab cooling

This paper presents the findings of a field study of occupant thermal comfort and thermal environments with a radiant slab cooling system. The study combined field measurements and questionnaires based on the ASHRAE RP-921 project protocol. A total of 116 sets of data from 82 participants were collected in summer and winter. The results reveal that occupant whole-body thermal sensations with radiant cooling were consistent with the PMV model. The main advantage of radiant cooling for thermal comfort was found to be reduced local thermal discomfort with reduced vertical air temperature difference as well as reduced draft rate. The survey results revealed that 14–22% of participants in the study reported local cold discomfort in the arm–hand and the leg–foot regions. The results indicated that there may be lower limits on air speeds acceptable to occupants. Statistical analysis indicated that occupant thermal votes were free of significant correlation with personal, contextual and psychological factors. Suggestions to improve the questionnaire and the field survey process are offered.

Design and control tradeoffs for rockbins in passively solar heated houses with trombe walls, direct gain and high solar fractions

Performances of active and passive rockbins are compared in Albuquerque, NM, Santa Maria, CA, and Madison, WI. The basic house is assumed to contain both Trombe wall and direct gain. The Trombe wall and direct gain are assumed to be optimally sized and controlled for each weather zone. It is demonstrated that, provided charging is done from the trombe wall, rockbins can be used to advantage in reducing the early morning auxiliary energy consumption peak common to passive houses with night setback thermostats. The paper also analyzes performance sensitivity to rockbin configuration (active, radiant slab top down charge, radiant slab bottom up charge), and to control strategies for charging and discharging. Effects of fan energy are included.