HEATING SYSTEM CONTROL BASED ON REQUIRED HEATING POWER

• US 20100059598A1
• Filed: 02/06/2008
• Published: 03/11/2010
• Est. Priority Date: 02/08/2007
• Status: Active Grant

• Current Assignee: Nordiq Goteborg AB
• Original Assignee: Nordiq Goteborg AB
• Inventors: Gummérus, Peter, Lindgren, Matts
• Granted Patent: US 8,086,353 B2
• Time in Patent Office: Days
• US Class Current: 236/91.E
• CPC Class Codes: G05D 23/1917 using digital means
• CPC Class Codes: G05D 23/1931 to control the temperature of one space

Abstract

A control system and method for controlling an indoor heating system for an indoor environment in accordance with a desired indoor temperature, comprising a sensor (18) for detecting an outdoor temperature, a sensor (17) for detecting a in return temperature T_return of a heat carrying medium circulated in a heat distribution system with a flow rate, and a controller (13). The controller is adapted to determine a required heating power P_req to be delivered by said heat distribution system to maintain a heating power balance according to P_req=P_loss−P_source, where P_loss is an approximation of heating power losses from said building, and includes a dynamic approximation of heating power transfer through walls of the building, based on at least said desired indoor temperature, said detected outdoor temperature, a heat transfer coefficient of the wall, and a heat capacity of the wall, and P_source is an approximation of heating power sources external to said heating system, and, based on the detected return temperature, control a combination of forward flow temperature and flow rate so as to ensure that the distribution system delivers said required heating power. According to the present invention, a dynamic model of the heating power balance of the building is used to control the heating power delivered by the heating system. This results in improved control compared a control scheme based only on flow temperature control based on outdoor temperature.

Claims

1. A control system for controlling an indoor heating system for an indoor environment in accordance with a desired indoor temperature, comprising:

a sensor for detecting an outdoor temperature, a sensor for detecting a return temperature T_return of a heat carrying medium circulated in a heat distribution system with a flow rate,

a controller adapted to;

determine a required heating power, P_req, to be delivered by said heat distribution system to maintain a heating power balance according to P_req=P_loss−

P_source,

where P_loss is an approximation of heating power losses from said building, and includes a dynamic approximation of heating power transfer through walls of the building, based on at least said desired indoor temperature (T_room), said detected outdoor temperature (T_amb), a heat transfer coefficient of the wall (kA), and a heat capacity of the wall (Mc_p), and P_source is an approximation of heating power sources external to said heating system, and

based on the detected return temperature, control a combination of forward flow temperature and flow rate so as to ensure that the distribution system delivers said required heating power.

2. The control system according to claim 1, further comprising a flow sensor for detecting said flow rate, and wherein the controller is adapted to control a forward flow temperature based on the detected flow rate.

3. The control system according to claim 2, wherein the forward flow temperature T_forward is determined according to the relationship

$T_{\mathrm{forward}}=\frac{P_{\mathrm{req}}}{c_p}$



flow + T return ,

where c_p is the specific heat capacity of the heat carrier, flow is the detected flow rate, and T_return is the detected return temperature of the heat carrier.

4. The control system according to claim 1, wherein the controller is adapted to control a mass flow rate based on a given forward flow temperature.

5. The control system according to claim 4, wherein the mass flow rate (flow) is determined according to the relationship:

$\mathrm{flow}=\frac{P_{\mathrm{req}}}{c_p<br><br>\left(T_{\mathrm{forward}}-T_{\mathrm{return}}\right)},$

where c_p is the specific heat capacity of the heat carrier, T_forward is the forward flow temperature, and T_return is the detected return temperature of the heat carrier.

6. The control system according to claim 1, wherein said controller is connected to a memory, storing parameters for defining a model of said heating power balance, said model enabling approximation of said heating power losses and heating power sources.

7. The control system according to claim 1, wherein said heating power transfer, P₁, from said indoor environment, is approximated according to:

P₁=2kA·

(T<sub>room—

sp</sub>−

T_wall),

where k is the specific heat transfer coefficient of the entire wall, A is the area of the wall, T<sub>room—

sp</sub> is the desired indoor temperature, and T_wall is the temperature in the middle of the wall.

8. The control system according to claim 7, wherein the controller is adapted to determine T_wall recursively according to:

$T_{\underset{t=n+1}{\mathrm{wall}}}=T_{\underset{t=n}{\mathrm{wall}}}+4·<br><br>\frac{\mathrm{kA}}{M_{\mathrm{wall}}·<br><br>c_p}·<br><br>\left[\frac{\left(T_{\mathrm{room\_sp}}+T_{\mathrm{amb}}\right)}{2}-T_{\underset{t=n}{\mathrm{wall}}}\right]·<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>t,$

where T<sub>room—

sp</sub> is the desired indoor temperature, T_amb is the detected outdoor temperature, k is the specific heat transfer coefficient of the entire wall, A is the area of the wall, M_wall is the mass of the wall and c_p is the specific heat capacity of the wall.

9. The control system according to claim 8, wherein the controller is adapted to use

$T_{\mathrm{wall}}$

( t = 0 ) = ( T room_sp + T amb ) 2

as a starting value.

10. The control system according to claim 1, wherein the control system further comprises a sensor for detecting actual indoor temperature, and wherein the controller is further adapted to apply a temperature control term based on said detected indoor temperature when determining the required heating power.

11. The control system according to claim 10, wherein said control term is

$P*(\varepsilon$

- 1 Ti * ∫

0 t 

ɛ

·



t ) ,

where ε

equals T<sub>room—

sp</sub>−

T_room, where T<sub>room—

sp</sub> is the desired indoor temperature and T_room is the detected indoor temperature.

12. The control system according to claim 6, wherein said model includes an approximation of internally generated heating power P_int as a constant according to:

P_int=kA·

Δ

T_eq,

where k is the specific heat transfer coefficient of the entire wall, A is the area of the wall, and T_eq is the obtainable difference between indoor temperature and outdoor temperature without any heating power contribution from the heating system.

13. The control system according to claim 6, wherein said model includes approximations of external heat power flows, including at least one from a group consisting of ventilation, sun radiation, tap water, electrical appliances and human beings.

14. A method for controlling an indoor heating system for an indoor environment in accordance with a desired indoor temperature, comprising:

detecting an outdoor temperature;

detecting a return temperature T_return of a heat carrying medium circulated in a heat distribution system with a flow rate;

determining a required heating power, P_req, to be delivered by said heat distribution system to maintain a heating power balance according to P_req=P_loss−

P_source, including;

approximating a heating power transfer through walls of the building, based on at least said desired indoor temperature (T_room), said detected outdoor temperature (T_amb), a heat transfer coefficient of the wall (kA), and a heat capacity of the wall (Mc_p), and

approximating heating power sources external to said heating system; and

based on the detected return temperature, controlling a combination of forward flow temperature and flow rate so as to ensure that the distribution system delivers said required heating power.

15. The method according to claim 14, further comprising detecting said flow rate, and controlling a forward flow temperature based on the detected flow rate.

16. The method according to claim 14, further comprising controlling a mass flow rate based on a given forward flow temperature.

17. The method according to claim 14, wherein said heating power transfer, P₁, from said indoor environment, is approximated according to:

P₁=2kA·

(T<sub>room—

sp</sub>−

T_wall),

where k is the specific heat transfer coefficient of the entire wall, A is the area of the wall, T<sub>room—

sp</sub> is the desired indoor temperature, and T_wall is the temperature in the middle of the wall.

18. The method according to claim 17, wherein T_wall is determined recursively according to:

$T_{\underset{t=n+1}{\mathrm{wall}}}=T_{\underset{t=n}{\mathrm{wall}}}+4·<br><br>\frac{\mathrm{kA}}{M_{\mathrm{wall}}·<br><br>c_p}·<br><br>\left[\frac{\left(T_{\mathrm{room\_sp}}+T_{\mathrm{amb}}\right)}{2}-T_{\underset{t=n}{\mathrm{wall}}}\right]·<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>t,$

where T<sub>room—

sp</sub> is the desired indoor temperature, T_amb is the detected outdoor temperature, k is the specific heat transfer coefficient of the entire wall, A is the area of the wall, M_wall is the mass of the wall and c_p is the specific heat capacity of the wall.

19. The method according to claim 14, further comprising detecting actual indoor temperature, and applying a temperature control term based on said detected indoor temperature when determining the required heating power.

20. The method according to claim 14, further comprising approximating internally generated heating power P_int as a constant according to:

P_int=kA·

Δ

T_eq,

where k is the specific heat transfer coefficient of the entire wall, A is the area of the wall, and T_eq is the obtainable difference between indoor temperature and outdoor temperature without any heating power contribution from the heating system.