Method for operating a water heater appliance

1. A method for operating a water heater appliance, the method comprising:

determining a temperature, T tank , of water within a tank of the water heater appliance, a temperature, T cold , of water at an inlet conduit of the water heater appliance and an actual position, VMP actual , of a mixing valve of the water heater appliance;

calculating a theoretical position, VMP theoretical , of the mixing valve of the water heater appliance, the VMP theoretical being a function of at least the T tank and the T cold ;

evaluating a difference between the VMP actual and the VMP theoretical , ΔVMP;

establishing a lower flow rate limit for water exiting the water heater appliance and an upper flow rate limit for water exiting the water heater appliance, the lower flow rate limit and the upper flow rate limit each being a function of at least the ΔVMP,

wherein the mixing valve of the water heater appliance is opeerable to mix water from the inlet conduit of the water heater appliance with water from the tank of the water heater appliance.

2. The method of claim 1 , wherein said step of determining comprises measuring the T cold by receiving a signal at a controller of the water heater appliance from a mixing valve temperature sensor positioned downstream of the mixing valve of the water heater appliance when the mixing valve of the water heater appliance is fully open or closed.

3. The method of claim 1 , wherein said step of determining comprises measuring the T cold by receiving a signal at a controller of the water heater appliance from a cold water temperature sensor positioned on the inlet conduit of the water heater appliance.

4. The method of claim 1 , wherein said step of calculating comprises calculating VMP theoretical with

VMP

theoretical

=

%

⁢

⁢

ColdWater

*

FS

+

A

where

%

⁢

⁢

ColdWater

=

c

p

,

h

⁢

Δ

⁢

⁢

T

tank

c

p

,

c

⁢

Δ

⁢

⁢

T

cold

+

c

p

,

h

⁢

Δ

⁢

⁢

T

tank

*

100

;

Δ

⁢

⁢

T

tank

=

T

tank

-

T

set

;

Δ

⁢

⁢

T

cold

=

T

set

-

T

cold

;

c p,h is the specific heat of water at T tank ;

c p,c is the specific heat of water at T cold ;

FS=B−A;

A is the input to the mixing valve at a fully open positon; and

B is the input to the mixing valve at a fully closed positon.

5. The method of claim 1 , wherein the lower flow rate limit and the upper flow rate limit are each univariate quadratic functions of the ΔVMP.

6. The method of claim 5 , wherein said step of establishing comprises establishing the lower flow rate limit with

f lower (Δ VMP )= a *(Δ VMP ) 2 +b*Δ+c

where

f lower (ΔVMP) is the lower flow rate limit; and

a, b and c are coefficients with 0<a≦0.5, −1<b<0 and 0.5<c<2.

7. The method of claim 5 , wherein said step of establishing comprises establishing the upper flow rate limit with

f upper (Δ VMP=d *(Δ VMP ) 2 +e*ΔVMP+f

where

f upper (ΔVMP) is the upper flow rate limit; and

d, e and f are coefficients with 0<d≦0.5, −2 <e< 0.5 and 1<f<3.

8. The method of claim 1 , further comprising estimating a flow rate of water through the water heater appliance based at least in part on the lower flow rate limit and the upper flow rate limit.

9. The method of claim 8 , wherein said step of estimating comprises averaging the lower flow rate limit and the upper flow rate limit.

10. The method of claim 1 , wherein the mixing valve is positioned within a casing of the water heater appliance.

11. A method for operating a water heater appliance, the water heater appliance having a mixing valve positioned within a casing of the water heater appliance, the method comprising:

determining a temperature, T tank , of water within a tank of the water heater appliance, a temperature, T cold , of water at an inlet conduit of the water heater appliance and an actual position, VMP actual , of the mixing valve of the water heater appliance;

calculating a theoretical position, VMP theoretical , of the mixing valve of the water heater appliance, the VMP theoretical being a function of at least the T tank and the T cold ;

evaluating a difference between the VMP actual and the VMP theoretical , ΔVMP;

establishing a lower flow rate limit for water exiting the water heater appliance and an upper flow rate limit for water exiting the water heater appliance, the lower flow rate limit and the upper flow rate limit each being a function of at least the ΔVMP; and

estimating a flow rate of water through the water heater appliance based at least in part on the lower flow rate limit and the upper flow rate limit,

wherein the mixing valve of the water heater appliance is configured for mixing water from the inlet conduit of the water heater appliance with water from the tank of the water heater appliance.

12. The method of claim 11 , wherein said step of determining comprises measuring the T cold by receiving a signal at a controller of the water heater appliance from a mixing valve temperature sensor positioned downstream of the mixing valve of the water heater appliance when the mixing valve of the water heater appliance is fully open or closed.

13. The method of claim 11 , wherein said step of determining comprises measuring the T cold by receiving a signal at a controller of the water heater appliance from a cold water temperature sensor positioned on the inlet conduit of the water heater appliance.

14. The method of claim 11 , wherein said step of calculating comprises calculating VMP theoretical with

VMP

theoretical

=

%

⁢

⁢

ColdWater

*

FS

+

A

where

%

⁢

⁢

ColdWater

=

c

p

,

h

⁢

Δ

⁢

⁢

T

tank

c

p

,

c

⁢

Δ

⁢

⁢

T

cold

+

c

p

,

h

⁢

Δ

⁢

⁢

T

tank

*

100

;

Δ

⁢

⁢

T

tank

=

T

tank

-

T

set

;

Δ

⁢

⁢

T

cold

=

T

set

-

T

cold

;

c p,h is the specific heat of water at T tank ;

c p,c is the specific heat of water at T cold ;

FS=B−A;

A is the input to the mixing valve at a fully open positon; and

B is the input to the mixing valve at a fully closed positon.

15. The method of claim 11 , wherein the lower flow rate limit and the upper flow rate limit are each univariate quadratic functions of the ΔVMP.

16. The method of claim 15 , wherein said step of establishing comprises establishing the lower flow rate limit with

f lower (Δ VMP )= a *(Δ VMP ) 2 +b*ΔVMP+c

where

f lower (ΔVMP) is the lower flow rate limit; and

a, b and c are coefficients with 0<a≦0.5, −1<b<0 and 0.5<c<2.

17. The method of claim 15 , wherein said step of establishing comprises establishing the upper flow rate limit with

f upper (Δ VMP )= d *(Δ VMP ) 2 +e*ΔVMP+f

where

f upper (ΔVMP) is the upper flow rate limit; and

d, e and f are coefficients with 0<d≦0.5, −2<e<0.5 and 1<f<3.

18. The method of claim 11 , wherein said step of estimating comprises averaging the lower flow rate limit and the upper flow rate limit.

19. The method of claim 11 , wherein the water heater appliance does not include a flow meter for measuring the flow rate of water through the water heater appliance.

20. The method of claim 11 , wherein said steps of calculating, evaluating, establishing and estimating are performed by a controller of the water heater appliance.