Jan Hensen University of Strathclyde, Glasgow |
Karel Kabele Czech Technical University in Prague |
POSTER ONLY of paper presented at 'Building Simulation 97', Prague, Czech Republic
ABSTRACT
The paper reports the first results of an ongoing project aimed at generating design information /knowledge for wet central heating (WCH) refurbishment in multi-family houses in Central Europe. In that practical context, integral modelling and simulation of a building and its heating system is demonstrated. Given the underlying importance of the dynamic thermal interactions, building and plant are modelled at a high level of resolution using the ESP-r energy simulation environment.
BACKGROUND
A large proportion of the Czech housing stock consists of multi-family houses, very often with a central (solid fuel) boiler, gravity circulation, and almost no temperature control at the individual apartment level.
Nowadays very often refurbishment takes place, involving replacement of the boiler (usually gas or oil instead of solid fuel), incorporating a pump and either central thermostatic control or thermostatic valves, while the pipes and radiators remain the same.
The system designer now faces the challenge to select a suitable boiler in terms of lightweight or cast-iron, condensing or non-condensing, originally specified capacity (i.e. oversized) or re-calculated, etc.
Some of the factors that should be considered include:
It is very difficult to predict in a general sense the impact of these factors on:
The current work uses computer modelling and simulation to focus on a (solid fuel) boiler that needed to be changed to a modern natural gas type. The main questions are:
MODELLING
The house in Prague.
Heating system schematic.
Boiler model parameters (base-case: conventional sized, heavyweight).
The aquastat of the boiler was set to 90 C. The boiler is ON/OFF controlled based on comparison of the temperature sensed in a reference zone with the set-point of the central thermostat.
ESP-r model of the building.
ESP-r model of the WCH system
Pump model parameters.
Radiator model parameters.
SIMULATIONS and RESULTS
Boiler configurations:
H = heavyweight; L = lightweight;
D = sized according prevailing design standards; O = over-sized.
Boiler code | HO | LO | HD | LD |
total mass [kg] | 1000 | 100 | 1000 | 100 |
fuel mass flow rate [kg/s] | .00126 | .00126 | .00076 | .00076 |
output [kW] | 55 | 55 | 32 | 32 |
RESULTS:
Gas consumption [m3/day]
HO |
LO |
HD |
LD |
|
Winter |
21.32 |
21.47 |
20.41 |
20.19 |
Spring |
16.48 |
17.24 |
14.97 |
15.24 |
Ave. |
18.90 |
19.35 |
17.69 |
17.71 |
% |
100% |
+2.4% |
-6.4% |
-6.3% |
Operational time [hours/day]
HO |
LO |
HD |
LD |
|
Winter |
4.70 |
4.73 |
7.50 |
7.42 |
Spring |
3.63 |
3.80 |
5.50 |
5.60 |
Ave. |
4.17 |
4.27 |
6.50 |
6.51 |
% |
100% |
+2.4% |
+56% |
+56% |
Operational water-side efficiency [-]
HO | LO | HD | LD | |
Winter |
0.91 |
0.91 |
0.97 |
0.97 |
Spring |
0.91 |
0.91 |
0.97 |
0.97 |
Ave. |
0.91 |
0.91 |
0.97 |
0.97 |
% |
100% |
-0.17% |
+6.9% |
+6.8% |
SIMULATION PERIOD:
A typical winter day (8 January) and a typical spring day (3 April), using a building-side computational time-step of 2 minutes, and a plant-side time-step of 1 minute.
CONCLUSIONS
In terms of the considered WCH heating system:
In terms of modelling and simulation:
Future work:
IN RETROSPECT:
Although various problems still require resolution, and despite the intensive effort required to effectively model a typical WCH system, we believe that integrated modelling and simulation of the building and plant is the way forward in addressing the related design and control problems of these systems.