In recent years, the significance of radiant heating and cooling systems has been rediscovered, and they are now widely adopted in buildings for various uses. Although radiant heating and cooling systems are usually operated intermittently in Japan, system design is based on the steady state heat transfer calculation. The purpose of this paper is to develop an unsteady state thermal simulation model of the space heated by a hot water floor heating system which has pipes buried in concrete and to analyze dynamic thermal characteristics of a floor heating system intermittently operated under design weather conditions. The obtained results are summarized as follows.
1) A simulation method for space thermal environment and heating rate of a floor heating system or air-conditioning system is proposed for the office space in which both the perimeter zone and interior zone are controlled separately. Heat exchange rate of water in the floor heating system is calculated using the fin efficiency proposed by Kollmar-Liese. In the space environment simulation model, it is assumed that there is a uniform heat generating surface at the buried infra-floor pipe level. Four points of air temperature, 11 points of space surface temperature and 2 points of heat generating surface in the floor are treated as unknown values in heat balance equations. There are two features in this simulation method. One is that in case operating temperature is controlled, for example, the weighting factors of operative temperature for excitation of hot water supply temperature are used. Using these weighting factors, the required hot water temperature to keep the operating temperature set point can be obtained.
The other is that floor heating system factor K is newly defined. The effect of floor heating on the space can be described by only two factors, i.e. floor heating system factor K and the hot water supply temperature.
2) A chart for determination of design hot water flow rate in any combination of pipe diameter and pipe pitch is proposed. A system designer can use this chart easily, calculating floor heating system factor K under standard conditions:
3) From the numerical analysis of unsteady state space environment heated by hot water floor heating system in intermittent operation, the following results are obtained.
a) In the case where the thickness of concrete in which pipes are buried is 100 mm, three hours is required for warming up in the space which has a normal envelop, two hours in the space with an adequately insulated envelop and four hours in the space with an uninsulated envelop or into which a large amount of infiltration comes.
b) To complete warming up in a very short time, it is more efficient to raise the hot water temperature than to increase the hot water flow rate.