HVAC Heat Pump

[redpoint5]

Originally Posted by Paulbstockton6@hotmail.co

Could you post a picture of the furnace spec plate?

ECM motors (variable speed) can be installed... (google time)....part costs less than $300.

I'm very interested in this aspect. Would be sweet if it varies automatically based on air temperature of the supply side. Move just the amount of air required to keep that temperature well within spec.

Assumption...not enough return air. Could you provide:
1. Measurements of both return ducts (ie: 16" or 20x25")

Both ducts are pictured above. The round return (upstairs ceiling) is 12" diameter and the square one (downstairs on the floor) is 17x20". Both grills and filters are 17x20"

3. Roof insulation depth or R-value. ( mine was R19; 8 inches fiberglass, I went balls out and it is now R70,;24-30" )

I needed to get in the attic for another reason, so I took a peek. The label says R38, but looking at the inches of depth it looks closer to R30. Maybe it compresses after 20 years?

4. Type of attic vent, est size of vent, soffit ( opinion as to whether attic ventilation can be improved?)

21x Standard 50in/sq vents. Knuckleheads added 3 more after I pointed out intake ventilation was inadequate.



Soffit vents are a joke. 2" round things with screens that have UPC tags on them covering half the intake. There are 2 of them spaced every 3' around the house.

5. Opinion on noise level from air rushing into return grilles. ( too noisy? )

Audible, but not loud.

[Paulbstockton6@hotmail.co]

17x20 is good for about 1600cfm and 12" is good for about 500cfm..... that checks out

Grille size 17x20 = 340sqin x 2 = 680cfm... problem
So the grille for the 12" round duct (capacitu = 500cfm) vs grille (680cfm) good.
Grille size for the 17x20 square duct (capacity = 1600cfm) vs grille capacity (680 cfm)..... not so good and this return is noises than the other.one.
So you have. .500+680cfm= 1180cfm. (Choked) for a 5 ton system which likely set to 1500 to 1700cfm....
What just happened...so now you will have excessive pressure (big deal, I'm in the same boat) This will make the blower motor work hard...drawing more amps.
I predict that if you tested static pressure you will be exceeding the .50wc spec.
The vents on the roof top are sufficient...the soffit are not. The total vent area, say 20x.5sqft =10sqft. You need roughly 10sqft soffit area, spread about the perimeter of the roof for your attic to vent properly...rather, the free area of the ridge needs to equal the free area of the soffit at the perimeter of the attic floor.

R30/38 would be minimum and I'll bet they recommend double that in current codes for new houses.

One problem with the ECM motors is that they do adjust speeds automatically....based on static pressure.....oops.... weren't we talking about that earlier.. I'm predicting high static pressure due to restricted return air....This might be an issue/might not.

So, since we are deficient in return air, look at the return plenum, or that 17x20 duct....can you tap into that and run an additional return somewhere where it might be benificial....?

[redpoint5]

What amount of airflow is called for with a 125,000 BTU 80% efficient furnace? It seems everything is engineered around the AC needs... but the furnace has way more tons of heating output than the AC has cooling.

Originally Posted by Paulbstockton6@hotmail.co

Grille size 17x20 = 340sqin x 2 = 680cfm... problem

What just happened...so now you will have excessive pressure (big deal, I'm in the same boat) This will make the blower motor work hard...drawing more amps.
I predict that if you tested static pressure you will be exceeding the .50wc spec.

The downstairs return is more noisy... actually when I went to replace the filter the first time, I found that ducting was not sealed with the wall, so it was mostly pulling unfiltered air from within the room where the furnace is. Perhaps that was left unfinished to gain sufficient airflow? I sealed it up so that all air goes through the filter from the living room.

I'll test the pressure and see where I'm at. Strangely, when I remove the air filters, the air handler draws more power.

Perhaps in the meantime I can install a higher flow filter?

The vents on the roof top are sufficient...the soffit are not. The total vent area, say 20x.5sqft =10sqft. You need roughly 10sqft soffit area, spread about the perimeter of the roof for your attic to vent properly...rather, the free area of the ridge needs to equal the free area of the soffit at the perimeter of the attic floor.

Soffit ventilation will be on my to-do list for this summer. Looks like I need about 25 of the 16x8" vents.

I just looked up the specs on my current soffit vents. 0.8 sq/in LOL. I'd need like 1,800 of them to be adequate. I think there's about 100 on the whole house.

In the summer, I have been opening the access door to the attic.

R30/38 would be minimum and I'll bet they recommend double that in current codes for new houses.

Maybe I'll add some rolls. Currently have blown in fiber. I'd want to engineer some walkways though as I'm in the attic often.

So, since we are deficient in return air, look at the return plenum, or that 17x20 duct....can you tap into that and run an additional return somewhere where it might be benificial....?

Maybe. There is access between the ceiling and the floor above. Seems difficult, and you probably don't put a return in an exterior wall. There's no crawlspace.

[aerohead]

Originally Posted by redpoint5

Technology Connections just released this video explaining that furnaces are massively oversized, and several methods to see how oversized your furnace is.

My furnace is a single-stage, meaning it's either on, or off. This makes calculating how oversized it is easy. On the coldest day this year (Jan 13), we hit a low of 16F and a high of 24F (about the coldest it gets here). I reviewed my furnace fan power consumption for that day, which came in at 5.56 kWh. My fan runs at almost exactly 700 watts, and only runs when the furnace is on.

My weather station
https://ambientweather.net/dashboard...b5b0a74/graphs

If my furnace ran at 100% capacity (on for 24 hours in the day), the fan would consume 16.8 kWh (24hrs x 700 watts).

So, my duty cycle on the coldest day is 5.56 kWh / 16.8 kWh = 30%

The furnace is rated at 100,000 BTU/hr, so 30% of that is 30,000 BTU/hr. That means that a 2.5 ton (12,000 BTU = 1 ton) heat pump would have just maintained heat running at 100% capacity.

The real problem I'm trying to solve is to even the temperature differential between upstairs and downstairs. It's typically 6-10 degrees cooler downstairs. With my furnace blower only running 10% of the time on average during the coldest month, there's not much mixing occurring.

My thought is to replace my 5-ton, 10 SEER AC unit and 80% efficient gas furnace/blower with an inverter heat pump. Inverter heat pumps can run at any output from about 35% to 100%. They are designed to run continuously instead of turning on and off. My assumption is that running continuously will keep the air mixing between upstairs and down, somewhat evening out the temperature differential. My other assumption is that I can close registers to force more heat downstairs without risk of stressing the ductwork since this system would be running substantially less pressure.

Other minor benefits include substantially less noise from the blower and furnace.

Other thoughts are to install a door between upstairs and down, and to increase soffit ventilation since mine is such a joke, leading the attic to get very hot in the summer.

In the 1970s, some addressed this issue by creating a 'chase', or vertical duct, with a low- power tube-axial fan, which would draw air from the up-stair's ceiling when the HVAC cycled off, and pull it downstairs, where it would diffuse it into the living space, mixing and blending, as a ceiling fan can do when it's rotation is reversed. Kind of a 'homogenator.'

[JSH]

Originally Posted by Isaac Zachary

I haven't watched the video, but in my situation I let the house cool off at night and also when I'm not there. It can take several hours to get the temp back up. So an oversized furnace is a good idea in my mind.

I do the same. My heating cycle is 69F @ 4:30 am to heat the house by the time we get up about 5:30. That holds until 7 am when it goes back to 67F for the day. At 4:30 PM we heat to 72 F until 5:00 PM. (5 pm is when my electricity switches to peak rate*). We hold 69F to 7 pm and let the temp drop to 67F for the night. (It takes hours for the temp to actually fall down to 67F) (That is the schedule Mon - Thursday when we are both at work)

Rates are: $0.08 from 9pm - 7am / $0.16 from 7am - 5 pm / $0.41 from 5 pm - 9pm

Originally Posted by Isaac Zachary

I'm not sure if I'd save any money if I had a heat pump since gas is about a third the price of electricity.

There is a HUGE difference in efficiency. A furnace is 80 - 95% efficient. Heat pumps are 250% - 300% efficient.

[redpoint5]

I switched the thermostat off last Thursday evening 3/14 and haven't run heat since then.

We'll need some heat the coming week, but I might just use the gas fireplace as needed.

I let the temp drop to 66 at night, but this past week I've been taking all the solar gain I can get, driving the temperature in the evening to 76, and it only drops to 71 by morning.

[JSH]

Originally Posted by redpoint5

The real problem I'm trying to solve is to even the temperature differential between upstairs and downstairs. It's typically 6-10 degrees cooler downstairs. With my furnace blower only running 10% of the time on average during the coldest month, there's not much mixing occurring.

My thought is to replace my 5-ton, 10 SEER AC unit and 80% efficient gas furnace/blower with an inverter heat pump....

Seems like the core of your problem is that you are trying to heat and cool a giant 2 story house with a single zone HVAC system. I've yet to see a house were that actually works with equal temperatures on both floors.

I seems the easiest solution is to split your HVAC by floor. You could do this by adding another ducted unit or by adding ductless heat pumps to one of the floors. (I would suggest the floor with less individual rooms.)

I replaced our 80% ducted furnace with a ductless heat pump about 7 years ago. I ended pulling that furnace out but shortly after I did that I thought about it and regretted that choice. The furnace could have been kept as a back-up or to supplement heating when the temperatures drop and the heat pump efficiency also drops.

[rmay635703]

Originally Posted by oil pan 4

The furnace must be sized for unusualy cold weather events unless you have robust backups.

Our corn / pellet stove was right sized for 5-15F, it would keep the house warmish down to -20F but its efficiency fell off a cliff running 100% continuously and ash output went up massively.

We would sort of run both gas and pellets in very cold weather which has the benefit of warmer floors while not going bankrupt on pellets

[Paulbstockton6@hotmail.co]

I see a couple options.
One is to buy a couple mini splits to supplement your upstairs cooling.
Two is to remodel a bit to greatly improve your duct system. Try to pipe in returns into increase circulation...you probably need twice as much cfm to the upstairs returns into the rooms. One method would be to chase a return into a closet to the attic and install ceiling returns. Another method, add jumper returns to the ceilings of both bedrooms and the great room.
One saving grace could be that the heater could later be changed to a lessor output...which means...
A good HVAC guy could look at your house and do a basic load calculation of each room and make a proposal to increase circulation, and the amount of air flow to each room needs. They are fairly good at this and it comes at a cost.... he will tell you what you need to know. If he's an older tech, he may be able to "derate" your furnace...something some guys won't do.
I'm guessing ventilating the attic properly might relieve some usage.
For your blower motor, you can get information by googling "ecm blower motor swap retrofit"

[redpoint5]

I found the following interesting. It basically says that HVAC manufacturers have no incentive to include efficient air handlers because they aren't factored into the efficiency rating of the furnace or AC. It also claims the added cost of an ECM air handler has a payback period of 2-3 years.

Simply improving air handler efficiency would save way more electricity than getting everyone to buy efficient refrigerators.

Because the annual fuel utilization efficiency (AFUE) calculation for furnaces considers only fossil-fuel use, not electricity use, fan motor efficiency receives little attention from furnace manufacturers. Moreover, air conditioner manufacturers have little incentive to improve fan motor efficiency, since the existing seasonal energy efficiency ratio (SEER) test protocol includes default values for fan motor power consumption that differ from actual fan motor current measured in field studies.

“Residential HVAC Fans and Motors Are Bigger than Refrigerators,” a paper presented at the 2002 ACEE Summer Study on Energy Efficiency in Buildings, examines the economics of improvements in furnace fan motor efficiency. Authors Harvey Sachs, Toru Kubo, Sandy Smith and Kalon Scott note that electronically commutated motors (ECMs) are 15% to 30% more efficient at high speeds than permanent split capacitor motors (the type of motor installed in 90% of all residential air handlers). At low speeds, ECMs are even more impressive, achieving twice the efficiency of permanent capacitor motors.

The study’s authors note that investments in improved fan motor efficiency will yield greater energy savings than investments in further AFUE improvements. Although most furnace manufacturers offer ECMs for only their top-of-the-line equipment, ECMs are cost-effective in all regions of the country, with a payback period varying from two to three years (see Table 2). Switching to an efficient fan motor would save the typical homeowner 790 kWh per year, more than the consumption of a 2001-compliant refrigerator. But, in the absence of a regulatory nudge from Washington, furnace manufacturers show little interest in making ECMs available to all furnace buyers.

Originally Posted by Paulbstockton6@hotmail.co

For your blower motor, you can get information by googling "ecm blower motor swap retrofit"

That was the first thing I started looking into, and didn't find enough info to make me comfortable swapping motors.

Here's some info I'm finding based on your search recommendation;

Brushless DC motors are inherently more efficient than PSC motors. “The Evergreen motor runs at 80% efficiency compared to 60% efficiency for a PSC motor,” claimed Mohalley.

When used in ‘constant fan’ mode, at low speed, the motor draws 100 watts or less.

“First you measure the watt draw of the old motor,” said Proctor. “Then you measure the static pressure in the supply plenum with the old motor running. PSC motors are usually set up with a cooling speed and a heating speed. In 95 percent of standard furnaces, there are four speed taps coming off the motor: high speed, medium high speed, medium speed, and low speed. The cooling speed is usually high speed, while the heating speed is usually medium high or medium.

EDIT: Searching Youtube for PSC to ECM replacement only shows the exact opposite. For some dumb reason, it seems people are only interested in going from an efficient motor, to an inefficient one.