Variable refrigerant flow system with capacity limits

1. A variable refrigerant flow system, comprising:

one or more outdoor units;

a first indoor unit of a plurality of indoor units configured to receive refrigerant from the one or more outdoor units, the first indoor unit configured to serve a first building zone;

a user input device configured to receive a user command requesting heating or cooling of the first building zone by the first indoor unit; and

a controller configured to:

receive the command from the user input device;

receive an indication of a current price of energy;

in response to receiving the command, generate a constraint on a capacity of the one or more outdoor units based on the current price of energy; and

control the one or more outdoor units to operate in accordance with the constraint.

2. The variable refrigerant flow system of claim 1 , wherein the controller is configured to remove the constraint after a capacity limit period elapses.

3. The variable refrigerant flow system of claim 1 , wherein:

the controller is configured to generate the constraint by multiplying a maximum outdoor unit capacity by a function of the current price of energy to determine a modified constrained capacity; and

the controller is configured to control the one or more outdoor units by preventing an operating capacity of the one or more outdoor units from exceeding the modified constrained capacity.

4. The variable refrigerant flow system of claim 3 , wherein the function is equal to one when the current price of energy is less than a threshold price and equal to a value between zero and one when the current price of energy is greater than the threshold price.

5. The variable refrigerant flow system of claim 4 , wherein the value is between approximately 0.4 and 0.8.

6. The variable refrigerant flow system of claim 1 , wherein the controller is configured to control the one or more outdoor units to operate in accordance with the constraint by optimizing a cost function bound by the constraint.

7. The variable refrigerant flow system of claim 6 , wherein the controller is configured to:

remove the constraint after a capacity limit period elapses; and

optimize the cost function over an optimization period longer than the capacity limit period and comprising the capacity limit period.

8. A method of heating or cooling a building, comprising:

operating one or more outdoor units to provide refrigerant to a plurality of indoor units, each indoor unit associated with a zone of a building;

receiving an input from a user requesting heating or cooling of a first building zone by a first indoor unit of the plurality of indoor units;

receiving an indication of a current price of energy;

in response to receiving the input, generating a constraint relating to a capacity of the one or more outdoor units based on the current price of energy; and

controlling the one or more outdoor units to operate in accordance with the constraint.

9. The method of claim 8 , further comprising removing the constraint after a capacity limit period elapses.

10. The method of claim 8 , wherein:

generating the constraint comprises multiplying a maximum outdoor unit capacity by a function of the current price of energy to determine a modified constrained capacity; and

controlling the one or more outdoor units comprises preventing an operating capacity of the one or more outdoor units from exceeding the modified constrained capacity.

11. The method of claim 10 , wherein the function is equal to one when the current price of energy is less than a threshold price and equal to a value between zero and one when the current price of energy is greater than the threshold price.

12. The method of claim 11 , wherein the value is between approximately 0.4 and 0.8.

13. The method of claim 8 , wherein controlling the one or more outdoor units comprises optimizing a cost function bound by the constraint.

14. The method of claim 13 , furthering comprising:

removing the constraint after a capacity limit period elapses; and

optimizing the cost function over an optimization period longer than the capacity limit period and comprising the capacity limit period.

15. A variable refrigerant flow system, comprising:

one or more outdoor units;

a first indoor unit of a plurality of indoor units configured to receive refrigerant from the one or more outdoor units, the first indoor unit serving a first building zone;

an occupancy detector configured to detect a presence of an occupant in a building zone; and

a control circuit configured to:

receive an indication from the occupancy detector indicating that the occupant is present in the building zone;

receive a current price of energy;

in response to receiving the indication, generate a constraint relating to a capacity of the one or more outdoor units based on the current price of energy; and

control the first indoor unit and the one or more outdoor units to operate in accordance with the constraint and provide heating or cooling to the building zone.

16. The variable refrigerant flow system of claim 15 , wherein the control circuit is configured to remove the constraint after a capacity limit period elapses.

17. The variable refrigerant flow system of claim 15 , wherein:

the control circuit is configured to generate the constraint by multiplying a maximum outdoor unit capacity by a function of the current price of energy to determine a modified constrained capacity; and

the control circuit is configured to control the one or more outdoor units by preventing an operating capacity of the one or more outdoor units from exceeding the modified constrained capacity.

18. The variable refrigerant flow system of claim 17 , wherein the function is equal to one when the current price of energy is less than a threshold price and equal to a value between zero and one when the current price of energy is greater than the threshold price.

19. The variable refrigerant flow system of claim 15 , wherein the control circuit is configured to control the one or more outdoor units to operate in accordance with the constraint by optimizing a cost function bound by the constraint.

20. The variable refrigerant flow system of claim 19 , wherein the control circuit is configured to:

remove the constraint after a capacity limit period elapses; and

optimize the cost function over an optimization period longer than the capacity limit period and comprising the capacity limit period.