Dominique Marchio

Room thermal modelling adapted to the test of HVAC control systems

Abstract This paper presents the development of a room model adapted to the study of the influence of the sensor position in building thermal control. The temperature measured by the sensor of a room temperature controller depends on its position in the zone. The more the room conditions are non-homogeneous, the more the temperature at the sensor position can differ from the “mean air temperature”. Models, currently used for control studies, are very simplified. They consider the room air as perfectly mixed. Other models, actually used for comfort studies, are on the one hand not adapted to the use for control studies, where dynamic models are necessary. On the other hand, they are not generic enough to provide a flexible and usable testing tool for room controllers. The important phenomena, to be represented in the model, are analysed experimentally and by detailed simulation. From this analysis, a detailed list of criteria for the development of zone models is obtained. The criteria are used to develop a new room model. The proposed model is able to distinguish between centre air and different sensor air temperatures with time variation. An application for a zone conditioned by a fan coil unit illustrates the model. Validations of the model are carried out in a real test room.

Energy-efficient gas-heated housing in France: predicted and observed performance

Abstract This report presents selected results of an analysis of data collected by GdF, the gas utility of France, during a project to monitor the performance of energy-efficient gas-heated houses and apartments in France. The data base includes the performance predicted at the design stage, as well as supplementary information obtained by questionnaire from the residents. 220 residences yielded sufficiently complete and reliable data to permit weather correction to be carried out by PRISM software. The results show, on average, fairly close agreement between the observed consumption C tot, obs and the consumption C tot, the (predicted according to the French procedure), although with some tendency towards overconsumption (or underprediction), C tot, obs being 6% higher than C tot, the . Among individual consumers there is much scatter, especially for apartments. Characterized in terms of the r.m.s. variation of the ratio C tot, obs / C tot, the , the scatter is 0.3 for single-family residences and 0.5 for apartments. The scatter appears to be mostly due to behavioural effects, as suggested by the large variation (almost 2 to 1) between highest and lowest consumption in a group of six identical row houses. A detailed comparison between predicted and observed PRISM parameters (heating slope, base level and balance temperature) is presented for a subset of 82 single-family houses where the uncertainties are sufficiently small. Most of the overconsumption arises from differences between predicted and observed values of the base level (hot water and cooking), whereas for space heating prediction and observation agree within one percent. An attempt to correlate the ratio C tot, obs / C tot, the with data from the questionnaire has remained inconclusive for the most part.

Simplified Model for the Operation of Chilled Water Cooling Coils Under Nonnominal Conditions

This study presents a cooling coil model for calculating energy consumption in air-conditioned buildings that has a minimal number of inputs. The model accurately determines the cooling energy rate and dehumidification energy rate under nonnominal conditions, and takes into account operation under variable air and water flows. In this manner, the model enhances the simplified ASHRAE Toolkit model without requiring more input data. The main assumptions are justified considering the common existing configurations of cooling coils in the air-conditioning industry. The parameters of the model are identified from only one nominal rating point. The model has been validated on a VAV facility with an average deviation of 5% for total energy rate. Errors are mainly due to the assumption that the coil is either completely wet or dry even if the surface is partially wet.

Influence of sensor position in building thermal control: criteria for zone models

Abstract This paper presents modelling choices adapted to the study of the influence of the sensor position in building thermal control. The model is implemented in a toolbox of dynamic models of HVAC components. It must be suitable for the optimisation and the test of controllers and control strategies by simulation and emulation. Due to the convective coupling between the zone and its particular HVAC system, the temperature measured by the sensor of a room temperature controller depends on its position in the zone. Usually, the sensor is situated on a wall or near the HVAC system (e.g. radiator). The influence of the position of the sensor is analysed experimentally and by detailed simulation for different types of emitters. From this analysis, a detailed list of criteria for the development of zone models, adapted to controller tests, is obtained. The criteria are used to develop a new, dynamic model, able to distinguish between the temperatures at the centre and at different sensor positions. The developed model is then applied to closed-loop tests with a simulated controller for the case of a zone equipped with an electric convector. The results are presented for three controller types and are compared with the result using a well-mixed model.

A semi-analytical model for serpentine horizontal ground heat exchangers

This article focuses on a particular type of horizontal ground heat exchangers (HGHE) which can be used as a heat source (or heat sink) for geothermal heat pumps. It consists of a long pipe buried about 1 m below the ground surface and arranged in parallel regularly spaced sections, forming a serpentine. This article proposes a model for such a heat exchanger, where the serpentine is discretized axially and a three-step calculation procedure is performed on each node. The axial fluid temperature variation in the pipe is first computed by using an implicit numerical resolution scheme. Then, heat transfer in the ground surrounding the pipe is obtained by using the analytical cylindrical heat source solution. In the third step, used for mid- to long-term simulations, thermal interference between parallel pipe sections is taken into account using spatial superposition. Finally, these solutions are coupled iteratively to obtain the axial fluid and pipe temperatures at each time step. The model is then validated using a full-scale experimental facility located in Orléans, France. Following a brief description of the facility, validation results are reported. The main validation test consists of supplying the HGHE with a constant inlet fluid temperature (40°C [104°F]) for a 200-h period in soil at an initial temperature of 7.5°C (45.5°F). After an initial transient period, the recorded outlet fluid temperature matches the model prediction within 1°C (1.8°F).

Progress on single-sided ventilation techniques for buildings

Single-sided natural ventilation is a free cooling solution which accommodates readily to most office building layouts. However, this technique is often ruled out by building designers since its ability to maintain comfort conditions is difficult to assess. Indeed, the cooling effect of this technique driven by wind and stack effects is highly dependent on outdoor conditions. This article intends to review the techniques of single-sided natural ventilation and the tools available to assess the performance of this technique. Then, the performance of single-sided natural ventilation is assessed for low-energy office buildings in two European climates. The methodology is based on the use of a building energy simulation program coupled with a recently developed correlation for single-sided ventilation. Several cases of office buildings are assessed, taking into account the main factors influencing the natural ventilation potential such as building loads, thermal inertia and orientation. For each building case, the energy-saving potential of a mixed-mode cooling system is analysed compared with the same building case with a full air-conditioning system. The comfort level of non-air-conditioned buildings is then studied for each building case. Finally, the impact of the window type on the performance of single-sided natural ventilation is assessed.

Dynamic model identification applied to the measuring of thermal static characteristics of buildings

Abstract This study is devoted to the measurement of thermal characteristics of buildings: heat loss coefficient, equivalent solar aperture, thermal resistance of walls and main time constants. A set of measured data, that is temperatures and heat flux, pass through a parameter estimation algorithm to give a thermal dynamic model of the studied system (building or wall). Then static characteristics are derived. Measuring procedures are described and case studies show results whose reliability, 10–20% precision, permit a valid energy diagnosis to be made of an unoccupied building and of existing walls.

Control design of open-cycle desiccant cooling systems using a graphical environment tool

The control design of open-cycle desiccant systems involves three operation modes (ventilation, evaporative cooling and desiccant cooling) and two control parameters (regeneration temperature and air‘ ow rate) to match the cooling load. Speci” c HVAC component models have been added to SIMBAD library to run in Matlab/SimulinkÒ environment. The control strategy is de” ned using State‘ owÒprogram which is a user-friendly graphical tool. The whole simulation tool is used to set an adapted control strategy. The energy consumption and performance of the desiccant system are investigated for different cases of building loads, thermal inertia and climate during the cooling period.

Neural predictive control for single-speed ground source heat pumps connected to a floor heating system for typical French dwelling

Ground source heat pumps connected to a floor heating system can offer high efficiency for heating and cooling. However, the inertia of the floor heating creates a thermal lag that can lead to discomfort with conventional controllers. For this reason, a neural predictive controller for single-speed ground source heat pumps systems was developed. The objective of the controller is to minimize the energy consumption and maintain a good comfort level anticipating the thermal behavior of the building and external disturbances. A new neural network module for the heating power prediction of a single-speed ground source heat pumps system is proposed. The operation of the controller has been tested by simulation on a typical French dwelling during the month of March. In addition to an increase of comfort, numerical results showed that the predictive controller can provide up to 18% energy savings with the studied building in comparison with conventional controllers. Practical Implications: Ground source heat pumps are currently equipped with conventional controllers that are not necessarily suited for such systems, leading to overconsumption and discomfort. In the medium term, ground source heat pumps could be equipped as standard with predictive controllers as presented here. Further work needs to be done to evaluate the feasibility of such an implementation as regards the return on investment and the controller’s robustness.

Variable-speed air-to-air heat pump modelling approaches for building energy simulation and comparison with experimental data

The decrease in heat demand in low energy buildings and the development of new heating, ventilation and air conditioning systems call for a re-examination of the usual modelling approaches in building simulation. A comparison methodology is developed to confront different modelling approaches with experimental data. The methodology is applied to four models of variable speed air-to-air heat pumps. Two classical empirical models (a static and a dynamic one) and a detailed physical model are selected. Moreover, a simplified physical model is developed for this study. The detailed control of the experimental heat pump and a model of the defrost cycle are given. The four modelling approaches are compared to in situ measurements for outdoor temperatures between and including defrost phases. The simulation results are analysed from the point of view of building energy simulation.