Heat pump in Wash DC?

[mrkrupa]

(I posted this in GENERAL by mistake)

I have a Carrier Weathermaker gas unit in my basement. It appears to be high efficiency using large bore pvc for air in and exhaust. It has an evaporator coil mounted on top connected to a 21 year old Carrier compressor (38EB048350, couldn't locate info on it. Any help?). I don't know if the evaporator is as old as I can't see it. It may have been upgraded when the furnace was installed. Out of curiosity, what was a "high" efficiency seer rating 20 years ago?

The house is a Capital Hill town house built around 1912.

Put some gauges on the compressor and it had what seemed like a low discharge pressure, about 150. Suction was around 45 and suction temp about 50F. I expect that the unit is close to done if not over.

Learned a lot in the last few hours reading over the postings and thought I seek some specific input regarding efficiency and equipment selection.

I expect to stay here 20 years or more.

While I have the high eff natural gas furnace, I don't think the blower is VS. How much would a VS unit contribute to efficiency? Comfort?

I live in Washington DC? Is a heat pump an economical choice, considering I already have a HE furnace?

What about modding the blower? Are there retrofit kits for this kind of thing to convert to VS or do you have to buy an entire furnace (since this blower is part of the existing furnace)?

The ducting is at least as old as the AC and it is sheetmetal insulated with board (inside) through the crawl space. The radiator system has been replaced with forced air and the duct work serves double duty for forced hot air and cool air. The first floor comes up through the floor vents and the second down from the crawl space.

Electricity here runs me about 10 cents per kwh. They deregulated and now have complex bills itemizing production and distribution charges. I simply divided the dollars by the kwh's.

I'll search for opinions on Goodman and others but feel free to name drop. Thanks. What a resource!

Paul Krupa

[docholiday]

There is no way to modify your exsisting furnace, it is what it is. That said, I would keep the gas (replace the furnace) but opt for a heat pump which would give you the best of both worlds.

You already have a 90+ gas. Stay with it since venting is going to be an issue with anything less. Install a new furnace with an ECM motor. You can choose single or two stages, it really is not that big of a deal since it is going to only be used at the lower outdoor temperatures. The ECM motor will add to the efficiency of the heat pump you will be installing in place of that old air conditioning system.

Now, if Comfort is your bag, replace the furnace with a mod90 by Rheem and then install a 16 or 18 SEER, 2 stage a/c for optimum comfort. Granted you dont get the savings of a heat pump, but you'll be the envy of the neighborhood.

[junkhound]

Re: "Put some gauges on the compressor "

Some here will blow you away unless you have an EPA cert., so say so if you do and register as a pro. Otherwise, tongue in cheek, if no lic, you a bad boy, just did something illegal.

Per your request for advice, Go for the heat pump. Just looked at a natural gas newsletter today and the price (Sept 22) is over $14 MMBTU (about $1.35 hundred cu ft. at the distribution point), that equates to well over $2 therm soon if the price holds for residential natural gas -- OUCH!! Even at 10 cents kW-hr, you will save big $$$ going HP, GSHP even better, but likely not feasible in your location.

[mrkrupa]

Yes, I have an EPA cert. I work on container ships and operate and maintain reefers as well as the package units that cool down the boxes. I didn't sign up for the professional because I guessed it was more for the domestic HVAC industry which I know very little about.

Thanks for the advice. I have spoken to a few salesmen here in DC but they just wanted to replace the outside unit.

What about the duct work? I've read a lot on these pages about the integrity of the ducting being a large factor to realizing the full potential of the system. The insulated stuff in the attic seems pretty cold to the touch. How do you close leaks? Tape? I read about the airborne sealants. Any comment on those?

Paul Krupa

[BaldLoonie]

The EE was a nice unit -- for the early 70s! SEER is LOW by today's standards though.

What are your gas rates? That will tell if an add on HP will save.

Suction pressure and temp are both low. Airflow issues?

[mrkrupa]

Yeah, the airflow may have a problem. I can see at one time there was an electronic filter but it's gone now and no filter box to replace it. I opened the unit and found a couple pieces of filter media, pretty corse laid on the inlets of each side of the blower. I'm guessing I've got a pretty dirty coil. Other than tearing into it, I can't see it very well, if at all. But judging by the "feel" of the air at the registers it's pretty light. I suspect the coil has been changed more recently as there is nice new tape on the box and what looks like a pretty new txv.

Gas is about 37-45 cents per therm. Is there a simple formula for comparing the two or do I need to get my books out? I did a little research at the gas company. My bills indicate that several months my gas went as high as 79 cents per therm!

Thanks.

Paul krupa

[Edited by mrkrupa on 09-24-2005 at 12:13 AM]

[BaldLoonie]

You better check again. I'd be shocked if you are paying that little for gas!!!

[mrkrupa]

Yes Baldloonie, you are correct. Just invert those figures. The range should be 1.36 to 2.70 per therm. I'm waiting on my gas company's web page to get the historical average. It shows that I paid 1753 for the past twelve months and used 1101 therms for a 12 month average of $1.60 per therm. Lot's of variation on the so-called delivery charges. I also have a tankless gas water heater and a gas clothes dryer that would impact the analysis of HP calculation.

Any ideas on getting temperture information for any particular locale? I'll try a google search.

Thanks.

Paul Krupa

[Edited by mrkrupa on 09-24-2005 at 12:37 PM]

[dan sw fl]

Originally posted by mrkrupa
Any ideas on getting temperture information for any particular locale? Paul Krupa

[Edited by mrkrupa on 09-24-2005 at 12:37 PM]

Andrews AFB Bin Data
...................... < 65
'F ... July.. Annual Degree Hours
95 ... 3..... 6
90 ... 25.... 72
85 ... 76.... 243... Cooling Hours
80 ... 121... 428... 749
75 ... 157... 631...
70 ... 208... 925...
65 ... 114... 858...
60 ... 34.... 755... Heating Hours
55 ... 5..... 688... 6880 4827
50 ... ...... 671... 10065
45 ... ...... 665... 13300
40 ... ...... 734... 18350
35 ... ...... 708... 21240
30 ... ...... 621... 21735
25 ... ...... 362... 14480
20 ... ...... 212... 9540
15 ... ...... 101... 5050
10 ... ...... 51.... 2805
5 ... ...... 14.... 840

8745 124285 Degree-Hours< 65'F
5,179 Degree-Days < 65'F