Bryant Legacy heat pump low temp operation/accessory kit

ethicalpaul

Hi folks-
My mom's house in southern NY state has a Bryant "Legacy" heat pump (Puron refrigerant I think) hooked into an oil burning furnace.

It is set up to use the heat pump as the primary heat with the oil burner as "aux heat" on the Honeywell thermostat. I went into the thermostat's installer options to see that the switchover from "heat" to "aux heat" occurs if it's below 30F outside (it does have an outside temp sensor on it)

I have looked in the manual for the heat pump and it indicates that the heat pump can actually work down to like -20F if it has something called an "accessory kit" on it. Can someone tell me what this kit does and how can I tell if it's installed?

One guess I have is that the accessory kit has supplemental heating for the heat pump for when ambient temp drops?

I'd rather use electricity even when the efficiency drops a bit since I have her on a reduced "electric heating" rate and also I want to see how much electricity she can use to determine if solar is a good option for her house.

So the real question is "in how low an ambient temp can I run this heat pump and have it make sense"?

Thanks!

JUGHNE

What are the parts in the kit?

EBEBRATT-Ed

I would think the accessory kit is probably something to help the heat pump defrost at lower temps. Maybe just a wind baffle. Do you have a wind baffle now?

I would think oil would be better than electric at low temps. The colder it is the less a heat pump can do and at low temps they revert to defrosting which puts it into AC mode and cools the house

You could always put an electric duct heater in the oil furnace discharge. How much electric heat you can put in depends on if you have enough electric power available (obviously) and the CFM that the oil furnace can move

ethicalpaul

JUGHNE said:

What are the parts in the kit?

That's what I'm asking

The only info I have is the mention of "with accessory kit" in the manual

ethicalpaul

EBEBRATT-Ed said:

I would think the accessory kit is probably something to help the heat pump defrost at lower temps. Maybe just a wind baffle. Do you have a wind baffle now?

I don't know if I have a wind baffle. Is it an external thing that I can see? I don't have any external structures.

I would think oil would be better than electric at low temps. The colder it is the less a heat pump can do and at low temps they revert to defrosting which puts it into AC mode and cools the house

I can get behind this but there is crossover range I think. I'm willing to flirt with the lower end of this range. What is "low temps" to you?

You could always put an electric duct heater in the oil furnace discharge. How much electric heat you can put in depends on if you have enough electric power available (obviously) and the CFM that the oil furnace can move

I don't think I'd do that. What I'm wanting to do is anything "reasonable" to keep the heat pump operational in lower temps (yet to be defined). I'm not interested in resistive electric heat (unless in small doses to keep the heat pump working).

The manual also mentions supplemental heating being available in the heat pump, but I don't know if my model has it, and I don't know how to see or control when it comes into use.

JUGHNE

Why do you want to punish mom with more lukewarm heat pump "heat"?

ethicalpaul

I want to not punish mom with high energy bills

As long as her thermostat reads "70" and she has her nice warm slippers on, I'll be able to sleep at night.

I could install a nice steam system I suppose, but for today it's "lukewarm heat pump heat" vs "scorched air" so pick your poison

JUGHNE

You could reprogram the tstat 5 degrees lower to 25 before change over occurs.
Keep lowering it weekly until mom calls you. At that point she should be able to go to emergency heat setting for oil only.
This depends upon the BTUH size of the heat pump unit.

Typically HP's can run to very low temps as the supplemental heat is usually downstream of the HP coil.
At that time the HP is just preheating the air going to the heating elements.

With your fossil fuel setup, obviously it is one or the other for heat source.

ethicalpaul

Perfect, thanks. I must confess I already lowered it to 25 last time I was there to see how that would work. She hasn't called yet. The thermostat has a BUNCH of other programming in it so I think it will also go to AUX HEAT (oil) if other conditions occur, like if it can't keep up.

It's been such a mild winter so far it's probably 6 of one, .5 dozen of the other.

Just wondered what the industry (as represented here) thought about it, and wondered if I could hurt the heat pump.

She also has a fireplace, but I hate the waste of fireplaces and I want to put a nice insert in there or even a wood stove.

Illinoisfarmer

Looking at the Product Guide for the Legacy Series, the lower right corner of the first page mentions low ambient cooling down to -20 with an accessory kit. I'm wondering if the literature you're looking at doesn't specify low ambient cooling even though that's what they are referring to.

https://www.totalcomfortmech.com/hubfs/Bryant/PDS215B-03.pdf

As far as the ideal changeover point, we have a house on one of our farms that is rented out - the system is an air to air heat pump with an LP Furnace backup. The heat pump works great down to about 25 or 30 degrees - most of the time. If the wind speed and direction are just perfect, about 40 degrees seems to be the bottom end before the LP furnace is needed. Obviously, the lower performance of the HP, coupled with the increased heat loss varies not only with the outside temperature, but with the wind.

Our solution was to increase the changeover temp to 40. This isn't ideal, but neither is having cold, unhappy renters. If I was living there, I'd probably play with it when necessary and buy less LP. I suggested this, and they just wanted it to 'work all the time'.

Just my two cents worth. Have a good day!

ethicalpaul

Thanks! If I had renters I'd put it up there too

EBEBRATT-Ed

I would think 25 deg is about right. Maybe they don't use wind baffles anymore. It was just a pc of sheet metal that surrounded the outdoor coil to keep wind off the coil. Probably using variable speed condenser fan motor

SuperTech

I would avoid running the heat pump below 30 degrees if an oil fired furnace was available.  Below freezing temperatures the heat pump will definitely struggle and defrost more frequently.  This will put unnecessary wear on all of the components of the system, especially the compressor and the rest of the outdoor unit. 

I understand you want to heat the home while spending as little money as possible, everyone does. But wear and tear on the equipment and cost of repairs/replacement must be considered.  

A dual fuel system is far superior to an all electric air to air heat pump.  I installed one with a Thermopride oil furnace for my fathers house. He barely uses any oil and hasn't noticed any difference in his electric bill. I also see far fewer service calls on dual fuel setups. When the outdoor temperatures are the lowest we always get calls for typical heat pump systems not keeping up or freezing up. Why deal with that if it can be avoided?

retiredguy

In my last house just north of Pittsburgh, Pa. i had the exact same set up using a Bryant heat pump and an oil furnace. yes, it was an older model but the operation should be the same. I set the outdoor temp sensor change-over control to 20 degrees F which worked good for my installation. You do understand that a heat pump is just an A/C unit running backwards, the same as you would get if you put a window unit in a window in reverse. (it is now trying to cool the outside air). The "accessory kit", is probably just what we used to call a low ambient kit that was used to modulate or shut off the outdoor units fan to help control the refrigerant pressure in that coil. This would allow the unit to operate at a lower outdoor temperature.

The heatpump/oil furnace set-up is not the best choice for an electric and fuel heating system since when the outdoor unit defrosts and it switches to regular A/C mode to defrost the outdoor coil. At this point, the air to the house will get cold since it takes a short while to get the oil furnace to heat up. That said, I would call Bryant or one of it's dealers for their input on the most efficient way to run your mom's set-up and their recommendation for the lowest setting of the outdoor switchover sensor.

ethicalpaul

Thanks @EBEBRATT-Ed , @SuperTech and @retiredguy !

TAG

OP -- Are you sure the kit is for heating. And not low temp cooling ? Where are you reading you need the kit for heat pump operation? It's been a while since I did the "Legacy" model but, I don't remember needing anything special other than having it up on feet. (I always use Carrier/Bryant in my projects)

There will be chart showing the performance curve and another with some reference to the COP of the unit at various temps -- you can plug in the local electric rate at the various temps and COP and make the comparison to oil. The charts will show where the unit will start to fall off as far as output.

I have used the higher cost 5 speed model in the last couple projects -- it's a better fit for my mid-atlantic climate .... That unit still has full output down to 2 degrees. So if it's properly sized the only limiting factor is if it is still cheaper to run vs the other fuel. Don't confuse operating range and performance.

unclejohn

This is the listed accessories for the Bryant Legacy HP.
ACCESSORIES
ORDER NUMBER DESCRIPTION 018 ---A 024 ---A 030 ---A 036 ---A 042 ---A 048 ---A 060 ---A
HC32GE229 BALL BEARING MOTOR X X X
HC38GE228 BALL BEARING MOTOR X X
HC40GE228 BALL BEARING MOTOR X X
KAACH1701AAA CRANKCASE HTR X X X
KAACH1401AAA CRANKCASE HTR X
KAACH1601AAA CRANKCASE HTR X
KAACH1201AAA CRANKCASE HTR X
STANDARD CRANKCASE HTR S
KSACY0101AAA CYCLE PROTECTOR X X X X X X X
KAAFT0101AAA FREEZE THERMOSTAT X X X X X X X
KSAHS1701AAA HARD START X X X X X X X
KHAIR0101AAA ISOLATION RELAY X X X X X X X
KSALA0301410 LOW AMBIENT PSW X X X X X X X
KSALA0601AAA{ MOTORMASTER 230V X X X X X X X
KHAOT0201SEC OUTDOOR THERMOSTAT X X X X X X X
KHAOT0301FST OUTDOOR THERMOSTAT X X X X X X X
KHALS0401LLS SOLENOID VALVE X X X X X X X
KHASS0606MPK* SNOW STAND RACK X X X X X X
KSASH0601COP SOUND BLKT X X X X X X
KSASH2101COP SOUND BLKT X
KAACS0201PTC START ASSIST PTC X X X X X X X
KSASF0101AAA SUPPORT FEET X X X X X X X
KAATD0101TDR TIME DELAY RELAY X X X X X X X
KSATX0201PUR TXV PURON HSO X X X
KSATX0301PUR TXV PURON HSO X X
KSATX0401PUR TXV PURON HSO X
KSATX0501PUR TXV PURON HSO X
x = Accessory S = Standard
* Available through RCD.
{ Required accessories include ball bearing fan motor, compressor start assist (CAP / Relay), crankcase heater, evaporator freeze stat, isolation relay, hard
shut ---off TXV or liquid line solenoid valve.
ACCESSORY THERMOSTA

I think you would have to go to variable speed compressor to run and heat well below 30* F

JUGHNE

IMO, all those accessories sound to me to be for low ambient cooling (AC) operation.

SuperTech

At my fathers house I set the heat pump to not operate below 35 degrees, the Thermopride oil furnace takes over from there. I wired the heat pump so it won't switch on the furnace if it does need to defrost for some reason (it shouldn't in 35+ degree outdoor temps). This avoids all the negative things that come along with short cycling the oil burner. 

JUGHNE

Also with a fossil fuel set up for heat pumps, when it does do a defrost, the head pressure that shows on the compressor will almost scare you.
Think about it, it is then operating as a cooling AC, there is a fire burning under the inside coil that usually sees about 70 degree air. The outside coil that would usually shed that heat does not have a fan moving air at that time....it just sits there steaming.

You can hear the compressor strain.

With the conventional air handler, the aux electric heat that comes on during defrost is located above the inside coil. Not an oil/gas fire under it as with dual/fossil fuel design. Those compressors do not sound as painful at defrost.

Jamie Hall

I'm a simple minded soul. And I simply can't see the point in trying to run an air to air heat pump -- never mind air to water -- if the outside temperature is low enough to require defrost on the outside coil. Never mind the efficiency considerations, since that equation varies with how one's electricity is generated. Nor the cost considerations, since that varies with how much one's fuel and electricity costs.

But... switching the system to run in reverse to defrost that outside coil? The heat to do that comes from the house, where you just spent good money to put it. Really? And if you have to switch on electric resistance units to keep the occupants from freezing while you're doing it, where does your efficiency and cost go?

But... ? Yes, it will work. But does that mean that it's the best way to do it? I can tow my 15,000 pound stock trailer with my son's Honda Civic, too, or I could if I did something creative with the hitch -- but is it the right equipment for the job?

ethicalpaul

Even if, even with the defrost, it costs less to heat the house than using oil under 35F does? 

And I’m not sure it does, but I’m trying understand the limits of your thinking here

Jamie Hall

Mostly aesthetic, @ethicalpaul . And very limited! And, as I said, I'm not considering either efficiency or electricity source -- that throws a huge complexity into the question of what's "best", even if one can define "best" in any usable way... nor into the question of cost, since that varies all over the place. Just engineering elegance...

WMno57

ethicalpaul said:

Even if, even with the defrost, it costs less to heat the house than using oil under 35F does? And I’m not sure it does, but I’m trying understand the limits of your thinking here

Consider the total costs of ownership (TCO), not just the cost of fuel oil or electricity.

Equipment has a limited life span. Mean Time Between Failure (MTBF).

We don't talk Dollars on the Wall. The units of currency portrayed in the following example are fictitious. No identification with actual units of currency is intended or should be inferred.

Suppose your Mom's heat pump (parts and installation) cost 10,000 Walloonies, and has a MTBF of 40,000 hours. Each operating hour, including defrost hours, costs 1/4 of a Walloony (a two bit Walloony), in addition to the electricity.

You recently posted a Heat Pump love note from The Atlantic. The article failed to mention TCO or MTBF.

ethicalpaul

MTBF is great when you are looking at a large data set. But we all know some stuff fails immediately and some stuff goes and goes. And some stuff that is dead simple and ought to last decades rots out in 7 years like a Burnham independence steam boiler.

This post is about my mom’s heat pump that came with her house and is 10 years old and how well it might run at various temperatures. There’s no purchase decision here.

WMno57

Your Mom's heat pump may run another 10 years, or the additional stress from defrost cycles may be the straw that breaks the camel's back. Let us know how it works out.

I have all kinds of old equipment that has lasted longer than products that can be bought today.

EBEBRATT-Ed

Just my opinion but I think running a heat pump at a temperature that requires a lot of defrosting beats the tar out of the equipment. I don't see the point in doing that. I would have it off at 25 degrees

ethicalpaul

EBEBRATT-Ed said:

I would think 25 deg is about right. Maybe they don't use wind baffles anymore. It was just a pc of sheet metal that surrounded the outdoor coil to keep wind off the coil. Probably using variable speed condenser fan motor

I do have the lowest heat pump ambient operating temp at 25.

WMno57 said:

Your Mom's heat pump may run another 10 years, or the additional stress from defrost cycles may be the straw that breaks the camel's back. Let us know how it works out. 

 I have all kinds of old equipment that has lasted longer than products that can be bought today.

I’ll let you know. How do we know what killed it when it dies?

and yes I know that some machines just keep running. I said that above 😅