EP1026449A1

EP1026449A1 - Maximum flow boiler

Info

Publication number: EP1026449A1
Application number: EP99830057A
Authority: EP
Inventors: S.P.A. Iaber
Original assignee: Iaber SpA
Current assignee: Iaber SpA
Priority date: 1999-02-03
Filing date: 1999-02-03
Publication date: 2000-08-09

Abstract

The basic operating principle of this system is to store energy in the form of hot water and then to recover it when needed. This boiler stores the water from the heating system and keeps it hot.

The tank for storing this water can be built from less expensive materials than the tank for storing the household water. The tank can also be built to specifications which are more suitable for the size of the boiler itself.

The fact that there is no heat exchange coil in the tank means that it has a larger storage capacity Since the water contained in this tank comes from the heating system, there is no need for devices which prevent the build-up of calcium inside the tank itself.

When water is drawn, the household water will then be heated by a household heat exchanger of an appropriate size. The build-up of lime can be prevented by using a bypass valve which skips the heat exchanger during the pre-heating phase.

Description

This boiler is based on the general operating principle of storing energy in the form of hot water, and "recovering" it for use when needed. The differences between this type of boiler and a traditional storage boiler are as follows:
1. This boiler stores the water from the heating system and keeps it hot. A traditional storage boiler stores the water from the household system.
2. The tank for storing the water can be built from less expensive materials than those used for building a household water tank. The tank can also be built to specifications which are more suitable for the dimensions of the boiler itself, without being restricted by the sectional area of flow, which is practically mandatory in the household system because of the pressure levels involved.
3. The storage tank does not contain a heat exchange coil, which provides a bigger storage capacity for the same outside dimensions.
4. Since the water stored in the tank is from the heating system, it does not contain any calcium since it is a closed system, and so devices for preventing the build-up of calcium inside the tank itself are not necessary.
5. When water is drawn from the household system, the output from the burner will be equal to the energy stored. The household water will therefore be heated by a household plate heat exchanger of an appropriate size. For example, we have increased the number of plates in our Max Flow boiler from 16 at 24000 kcal/h to 28.
6. Obviously, each time water is drawn from the household system, a pump will have to move water from the storage tank to the primary heat exchanger where it will be heated, and then move the water to the plate heat exchanger where it will transfer heat to the household water.
7. A cycle for pre-heating the water in the storage tank will be necessary.
8. One problem which could exist is if the water is particularly hard and causes calcium to build up in the household portion of the plate heat exchanger. This problem can be prevented by using a bypass valve which skips the heat exchanger during the pre-heating phase.
While this boiler was being tested, we were able to develop an operating cycle which would allow the boiler to operate with only 2 probes, one to monitor the water in the primary heat exchanger and the other to monitor the water coming out of the household system. The benefit derived from monitoring the household water outlet is that it gives us an actual real-time reading of the water temperature when it reaches the end user. In fact, while this system is very effective for large capacities, it does have limitations for smaller capacities because the water coming out of the household system can reach temperature levels which are too high. The output of the boiler together with the energy transferred by the stored water is too excessive for smaller household capacities. By placing a probe at the water outlet, we can modulate the output of the burner, and even switch it off if the temperature of the water is too high.
We were still left with the problem of how to monitor the temperature of the water in the storage tank. We therefore placed a probe on the boiler's primary system, which functions as follows: during the pre-heating phase where the temperature of the water in the primary system reaches the required level, we turn off the burner and allow the pump to circulate the water in the primary system so that it is thoroughly blended with the water from the storage tank. In this way, the temperature of the water in the primary system will be the same as the water in the storage tank.

DETAILED OPERATING PRINCIPLE

(See the enclosed hydraulics diagram)

The operating principle which we have described below involves only the controls for the different apparatus, and not the modulation or "production" controls (such as the differential analog switch or the limit thermostat), which are already performed by the microprocessor and are valid.

SUMMER OPERATION

When the boiler is turned on, the following operating cycle will occur:
1. The three-way valve will move into the household position, and the pump will turn on for 2'.
2. After 2', the primary probe will check the water temperature in the primary system. If the reading indicates that heat is required, the burner will be turned on. If the reading indicates that the water temperature is higher than the set point, the boiler will be put in stand-by mode.
3. Once the probe detects that the required temperature has been reached, the burner will be switched off, but without turning off the pump, which will circulate the water for approximately 2 minutes. If the temperature of the water drops again, the primary probe will immediately switch on the burner, otherwise the three-way valve will move into the heating position and the boiler will be put in stand-by mode.
4. If water is drawn from the household system (the household flow switch closes the contact), the pump, the vent and the burner will be immediately switched on. As soon as the household probe starts to detect an increase in temperature, it will be read against the set point which has been previously entered into the microprocesser, which will then determine whether to leave the burner on, modulate it, or switch it off.
5. While the water is being drawn, the household probe will monitor the water temperature at the outlet, and the primary probe will monitor only that the water in the primary system does not reach dangerously high temperatures.
6. Once the water has been drawn from the household system (the household flow switch will be in the OFF position), the burner will be switched off, and the pump will circulate the water for approximately 2 minutes to check the temperature of the water in the storage tank, and initiate another pre-heating cycle if necessary.

WINTER OPERATION

1. The three-way valve will always be in the heating position, unless there is a request for water from the household system, or for a pre-heating phase. If there is a request for heat via the ambient thermostat at the same time as the pre-heating phase or the household flow switch is on, these latter two take precedence over the ambient thermostat.
2. The request for the pre-heating phase or the household flow switch is the same as the equivalent situation during summer operation. At the end of the cycle, the three-way valve moves into the heating position.
3. The heating mode is automatically modulated in our boilers.

PRE-HEATING CYCLE

Pump on for 2'
Temperature in the primary system checked
Temp. < 62° (max output)
Temp. > 62° (max output)
> 47° (min output) > 47°
(min output)
3-way valve in
heating position
Gas valve on Stand-by
No modulation
With max temp. selector turned off at 77° C (equivalent to boiler T. of approximately 65° C )
With min temp. selector turned off at 62° C (equivalent to boiler T. of approximately 50° C)
Pump circulates in household system for 2'
Temperature check
Temp. < 62° C (max output)
Temp. > 62° C (max output)
Temp. < 47° C (min output)
Temp. 47° C (min output)
3-way valve in
heating position
Stand-by

AT THE END OF THE PRE-HEATING CYCLE

WHILE WATER IS BEING DRAWN

3-way valve in household position

Pump/vent turned on
Gas valve turned on
Household set point 65 +/- 3° C (max) 50 +/- 3° C (min)
Modulation on household probe and switched off if primary temperature = 90° C

WATER IS NO LONGER BEING DRAWN

IF HEATING IS TURNED ON

If there is a request for heat via the ambient thermostat:

Pump, vent and gas valve on
Boiler modulates at 80 +/- 3° C and switches off at 6° C above modulation.

Every 4 hours (time to be determined), the 3-way valve is in the household position and a pre-heating cycle starts independently of any request occurring for heat.
At the end of the pre-heating cycle, if there is still a request for heating via the ambient thermostat, the system switches to the heating phase.

Claims

This boiler stores the water from the heating system and keeps it hot.
The tank can be built from less expensive materials than the tank used for the household water. It can also be built to specifications which are more suitable for the size of the boiler without any restrictions whatsoever.
There is no heat exchange coil in the storage tank, allowing for a bigger water storage capacity.
Since there is no calcium in the water contained in this tank, there is no need for devices to prevent the build-up of calcium inside the tank itself.
When water is drawn, the output from the burner equals the energy which is stored.
If the water is particularly hard, calcium build-up can be prevented by using a bypass valve which skips the plate heat exchanger during the pre-heating phase.
We are planning a dual operating system, which functions according to climatic conditions (summer and winter).