Bryant Evolution - balance point help

[m kilgore]

duh....I wasn't talking during defrost.

[arc8]

I am looking for the best Economic balance point.

Think of this a constructive criticism reply.

First you needed to have done a HeatLoad calculation, especially by your contractor! You need this to figure out your particular thermal balance pt and your economic balance pt. And this brings me to, how in h-- did they figure out your equipment sized??? The Evolution is a great system, but it doesn't mean you are getting the best system for your house!!!

!!It's very important to sized a whole system and fit it to your existing home!!

Now the equipment: The economic balance pt must be less than your thermal balance point. But how would you know that if you don't have a LoadCalc to guide you!
With a loadcalc in one hand and the right equipment selected to meet the need for efficiency and comfort's sake, you can determine 1. how much the heat pump can handle (at what temp pt to shut off), 2. when you want the gas furnace to come on (at what temp pt to turn on), and 3. if supplemental heat is required (sometimes it cost less to run the heatpump and resistive heat together than a gas furnace to a certain pt.).

But i could be all wrong about this idea if the Hybrid Heat system has a minicomputer built-in to figure this all out!

Good Luck with your new Hybrid Heat!!

[dan sw fl]

How do you change the balance point?

With
__ NEW house,
__ ___ NeW equipment,
__ ___ ____ electric rate change, or gas cost decrease.

[Airmechanical]

duh....I wasn't talking during defrost.

duh, never say cant!



.

[OOC]

Arc8 - Nice way to tie together the two types of balance points.

About that minicomputer figuring it all out. I read in an online home magazine the other day that there is a system that allows you to tell the tstat what the cost per KWh you pay for electrcity and what the cost per therm you pay for natural gas, and it figures out what the economic switchover point is. Anyone hear of that? The article didn;t mention brand names, it just gave the impression that that methods is the standard for todays high end systems. I did not think this was the case, but figured someone must make a tstat that allows that. It's a simple calc for a minicomputer.

[adamsdp]

Here in SE Michigan, the D1.7 electric rate (space conditioning) for heat pumps is about $.065 for summer and $.037/kWh for winter. Where did
you get the Bryant Equipment specs from? Your calculations below look very helpful. Thanks.

Economic balance point is not hard to determine once you know your utility rates and
heat pump C.O.P. in the temperature range of interest.

Calculated Economic balance point is likely clsoe to the 3-ton 15 SEER/8.4 HSPF heat pump / 2,000 sq. foot residence Heating Balance Point.
Calculated Economic balance point does not accurately account for the defrost cycle.

S.E. Michigan
Electric Rate ... ... ... $0.11 / kW
= 100,000 BTU/therm / 3413 BTU/ kW = 29.3 kW/ Therm
$3.22 / 100,000 BTU

http://www.michigan.gov/mpsc/0,1607,...5189--,00.html

specific C.O.P. ascertained for BRYANT heat pump 286-036 ( assumed same as CARRIER Performance Series)
Effective cost = $1.15 at C.O.P. of 2.8 @ 27'F)

xxxxxxxxxxxxx
Natural Gas ... ... ... .. $1.00 / Therm
http://www.dleg.state.mi.us/mpsc/gas/rates/gasrates.pdf

Therm = 100,000 BTU
at 95 % efficiency .. $1.053 / 100,000 BTUh

K.I.S.S.

Economic balance point = ~ 33' F ... Moderate-High electric rate versus relatively low Natural Gas cost pushes the economic balance point
higher than I would have anticipated for a HSPF 8.4 system. C.O.P. at 22'F - 28'F seems to be LOW. Perhaps, someone has an accurate ARI rating in this range.
C.O.P. values below were interpolated from the 47'F - 17'F data to show cost comparison /Economic Balance Point.

Based on review BRYANT (CARRIER PERFORMANCE Series) equipment specs.
________________________ $3.22 $0.11 29.3

..'F C.O.P. Effective
47 __ 3.60 ___ $0.895
46 __ 3.56 ___ $0.905
45 __ 3.52 ___ $0.916
44 __ 3.48 ___ $0.926
43 __ 3.44 ___ $0.937
42 __ 3.40 ___ $0.948
41 __ 3.36 ___ $0.959
40 __ 3.32 ___ $0.971
39 __ 3.28 ___ $0.983
38 __ 3.24 ___ $0.995
37 __ 3.20 ___ $1.007
36 __ 3.16 ___ $1.020
35 __ 3.12 ___ $1.033
34 __ 3.08 ___ $1.046
33 __ 3.04 ___ $1.060
32 __ 3.00 ___ $1.074
31 __ 2.96 ___ $1.089
30 __ 2.92 ___ $1.104
29 __ 2.88 ___ $1.119
28 __ 2.84 ___ $1.135
27 __ 2.80 ___ $1.151
26 __ 2.76 ___ $1.168
25 __ 2.72 ___ $1.185
24 __ 2.68 ___ $1.203
23 __ 2.64 ___ $1.221
22 __ 2.60 ___ $1.240
21 __ 2.56 ___ $1.259
20 __ 2.52 ___ $1.279
19 __ 2.48 ___ $1.300
18 __ 2.44 ___ $1.321
17 __ 2.40 ___ $1.343

[adamsdp]

Thanks for your reply and I am trying to learn as I go, along with the contractor. I think hybrid systems are fairly new to this area as 3 out of the 4 contractors I had come out said that they had heard of heat pumps but weren't familar with them. The contractor I hired has the most experience in this area with heat pumps but is still learning. The Evolution thermostat does not calculate the best balance point but has a lot of other nice features as far as I can tell being a newcomer to this field. I will see if I can track down the LoadCalc software.

I am looking for the best Economic balance point.

Think of this a constructive criticism reply.

First you needed to have done a HeatLoad calculation, especially by your contractor! You need this to figure out your particular thermal balance pt and your economic balance pt. And this brings me to, how in h-- did they figure out your equipment sized??? The Evolution is a great system, but it doesn't mean you are getting the best system for your house!!!

!!It's very important to sized a whole system and fit it to your existing home!!

Now the equipment: The economic balance pt must be less than your thermal balance point. But how would you know that if you don't have a LoadCalc to guide you!
With a loadcalc in one hand and the right equipment selected to meet the need for efficiency and comfort's sake, you can determine 1. how much the heat pump can handle (at what temp pt to shut off), 2. when you want the gas furnace to come on (at what temp pt to turn on), and 3. if supplemental heat is required (sometimes it cost less to run the heatpump and resistive heat together than a gas furnace to a certain pt.).

But i could be all wrong about this idea if the Hybrid Heat system has a minicomputer built-in to figure this all out!

Good Luck with your new Hybrid Heat!!

[adamsdp]

Under the advanced settings there is a selection where you can choose a heat pump lockout temperature. I think it is under Advanced/Settings/Hybrid Heat. If you can't find it let me know and I will try it again at home and reply.
My default setting was none which I think means the heat pump would run as long as it could keep up with heating demands and then switch to the furnace if it could not keep up. I have set mine for 28 deg for now.

How do you change the balance point?

[adamsdp]

My contractor spoke with the local Bryant rep and he said that there are two schools of thought on the balance point for this area - SE Michigan. One is that you have no heat pump lockout temp selected and let the heat pump run as much as possible until it can't keep up and then the furnace will take over as the heat pump will be cheaper to run than the furnace at any outdoor temperature that the heat pump can provide heat for. The other school is that the defrost cycle uses a good amount of electricity and also to save wear and tear on the heat pump, a balance point of 28-30 is a good setting. My contractor said they don't have a long history of information to go on in this area about the wear and tear/defrost cycle but he is going to look for software to provide more guidance.

[tbox8098]

Since I am a BRyant rep please go to page 2 and read my reply. you are way overthinking this decision. I think a good train of thought for you is to lower it until it in not able to keep you comfortable and then move it up a couple of degrees.

If not please set it at 20 and go from there

[aaCharley]

There is no reasonable economic balance point where the fossil fuel furnace is more efficient than the heat pump, until it's about -10F outside, (equal to the furnace). Balance point is and always will be the point where there the heat pump can no longer satisfy the heating demand alone. When the room temp falls below the setpoint, you have fallen below the balance point, and will require back-up heating to maintain the same setpoint.

You write that:
"when the heat pump's COP is at .95 "

The factor that you have not consideed in your analysis is the Cost of Power.

However, the Conversion of Power (COP) is only one factor in the equation.
At lower temps the Heat Pump COP becomes very low - you sited 0.95.
If raw energy cost (BTU cost) from electricty is 2X the NG cost, the cross over point for the cost of home heating will not be the heat pump COP number.

Neither of those consider the "comfort factor" of having blowing hot air, and that is homeowner subjective.

[dan sw fl]

You write that:
... However, the Conversion of Power (COP) is only one factor in the equation.

C.O.P. = Coeffficient Of Performance

http://en.wikipedia.org/wiki/Coefficient_of_performance

[aaCharley]

Thanks for the correction and the useful link to the proper definition.

The coefficient of performance, or COP (sometimes CP), of a heat pump is the ratio of the output heat to the supplied work . . . .

Conversion of Power is not correct - just the way I think of it.

That COP number is variable, depending upon the outside air temp. The Wikipedia example uses a geothermal source which would have very little variability.