Dual Fuel systems (heat-pump w/ Fossil Fuel)

Unknown

By disappointed I suspect you mean what is considered the cooler than "normal" air coming out of the registers. The main reason they didn't do that well here was the fact that they were combining them with electric heat and if the HP wasn't working properly it would use the electric excessively and cost them a mint to run. A lot of it had to do with guys that didn't know how to repair them properly. You're right, a little education can go a long way if you're trying to teach someone who will listen. I hate that point at which you see them start to lose interest and their attention shifting elsewhere. I taught HVAC to adults for a couple of years. I know that look well. ;)

Jamie Pompetti_2

?

With the increase in fossil fuel pricing we have noticed that our customers have been inquiring about dual fuel systems. We have installed quite a few of the Carrier Infinity hybrid systems. Although, they are expensenive. We are now offering lower SEER equipment also in the same package.

The two we have installed this month we used the Honeywell 8000 touch screen, which operates the system as the manger of which systems runs, the Heat-pump or the furnace.

This stat. allows you to lock the heat-pump out at your discretion.

Finally the question!!!!!!!

At what temperature are you losing ground with your heat-pump and you should allow the fossil fuel to take over?



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Tony Furst

Balance Point

It's all about the system balance point and where it falls in relationship to fuel costs for the heat pump versus the fossil fuel costs. Basically a heat pump always puts out more heat than electrcity consumed it's just that as the outdoor temperature drops the output decreases. Consider that at 35 degrees you get 3 to 4 times as much heat versus electrical input but at zero degrees you get slighly more than 1 to 1. The manufacturer should have a balance point chart as part of their literature to help in making the decision.

Unknown

Hmmm,

I'd say that was a figure that would be unique to each installation. It would take a little experimentation to arrive at the most correct setting and I would be shooting for a number that is just above the point in ODT at which the HP can no longer keep up with the load. This usually requires a few trips to the location and good feedback from the owner. Start at 35* and go from there. The lower you can go the better naturally. I'm not familiar with these controls, can you explain how the defrost sequence works?

JaredM

Balance Point

Calculating the balance point is a useful exercise which will answer your question for the specific job at hand.

Draw a simple graph with BTU's on one axis and outdoor temps an the other axis. Now, draw a line representing the heat loss of the building that begins with 0 btu's at 68 degrees or so and ends at the total heat loss at your design outdoor temp.

Next you will need the performance data of your particular heat pump. The data should give you a capacity of your heat pump matched with your indoor coil at 47F and 17F. You can pretty much draw a line through and extending past those points on your graph.

Where the lines intersect is your balance point....the outdoor temp at which the capacity of the heat pump matches the heat loss of your structure.

Hope that helps.

BTW, we've been installing hybrid heat pumps for over twenty years and customers love 'em as long as they understand 'em. The best of both worlds.

-Jared

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Unknown

Interesting...

It certainly helped me. I have installed them in the past, the old Carrier stuff with the fossil fuel package.It's been years. I DO believe they are a good setup but unfortunately here in the Northeast they got a real bad rap (heat pumps) and are a tough sell now. Noone ever showed me how to graph them out like that. Do you find that setting them at the calculated figure works the best or do you need to do any more adjusting to dial them in tighter? Last question, when set at this figure, will they go into defrost at all? We used to set them so they would shut off and go on fossil before they required defrosting. That's how we arrived at the switchover setting. I'm thinking it was 40* but that seems a bit high to me now.

Bruce Stevens

All the ones I have seen arond here NH coast

have been between 35 and 40 but I understand that some of the newer equipment can go lower does anyone know if that is fact or fiction

Wayco Wayne_2

I've been doing

a lot of dual fuel around here. I set the balance point at 35 as a rule. The Honeywell 8000 has increments of 5 degrees so the other choices are 40 and 30 on each side of that. If the customer is really interested in saving money I go lower. If they are worried about comfort I go higher. WW

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JaredM

Defrost

Yes, they will go into defrost. Defrost cycles are the most common when the outdoor RH is high...such as during a period of rain.

I usually adjust the outdoor stat to just above the balance point...and I usually use a seperate fossil fuel kit from my preferred heat pump manufacturer. The kit I use has a defrost feature available that cycles the fossil fuel burner on/off to temper defrost air. The balance point usually falls at around 30F in my area. BTW, I am located in NY.

Heat pumps are not that tough a sell even here in the northeast. You do have to explain to the customer exactly what to expect from them so they are not disappointed.

-Jared

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Bryan_16

8000 stat

try the 8000 stat and you can eliminate the ff kit. I really like them, and customers enjoy touch screen.