Heat Pump not delivering energy savings

[coaster]

We own a split-level 1500 sq ft home with electric baseboard heating.We installed a Fujitsu

12RLS mini-split in September 09. The installer and the Home Energy Audit claim a 30% saving in

heating costs with this unit.

The energy audit revealed some air leakage areas and with that list and a little DIY I managed

to reduce the heat loss by 10% qualifying for additional Federal grant money plus the heat pump

grant. So, all things being equal, I would save 10% on heating costs?

On the upper lever we have 7 baseboard heaters totalling 7500 watts on digital thermostats.

These heaters are set at 5 C as the heat pump has been in heat mode for the past month. The heat

pump is set at 66 F or 18.8 C and the upper level is comfortable. The lower level is heated by 3

Convectair convection heaters set at an average of 20 C, set back at night, same as previous

years.

Now comes the problem/question. Our latest electric bill shows an increase in consumption of 106

kWh over the same time period last year. The average outdoor temps for both periods are about

the same. I'm not looking forward to -10, -15 C when I have to add supplementary heat.

Changes from last year.

-heat loss reduced
-upper level baseboards essentially off
-heat pump installed
-increased electrical comsumption

What am I missing or doing wrong here?

Do I shut the unit off until cooling season arrives and heat with baseboards?
Do I turn the baseboards on and put the unit in fan mode for air circulation?
Do I lower the temp setting on the unit even lower?

Any assistance would be appreciated and apologies for the lengthy post.

[57]

This unit has a very good HSPF:

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

http://housesmartheating.com/hp-faq.html#2

This means that on average, it will be about 2-3 times as efficient as radiant heat. However, the efficiency does drop off as the temperature drops. Also 106 kWh in a couple of months is not much difference if your typical use is say 2000 kWh+... What was your overall usage when you saw the 106 kWh difference?

A small change in indoor requested temperature or in the heating degree days (outside temperature) and you'd see that much change. If you have the exact weather data, then you may be able to compare but to simply say the weather was about the same is not accurate enough.

If you've still got baseboards downstairs on, then that heat will rise and the split heat pump doesn't really need to work that hard - at it's minimum inverter rate it's only using about 900 Watts (3.4 W/BTU/h) So, this is really a supplemental unit which may only affect some (small) percentage of your overall electrical usage. There are other factors that also come into play in your electrical usage - stove, DW, dryer, etc...

You/they have overestimated how much savings you'll get from this unit since it's only supplying a (perhaps small) portion of your overall use.

You should continue to use your unit down to -10C since it's more efficient than radiant heat, however, you should monitor your overall usage for the entire winter to see how things go. Where is the heat pump located? If it's upstairs, then it'll not affect the downstairs usage very much since heat rises and it'll only affect a small portion of your overall usage, again because heat rises.

[Sylvain]

Originally Posted by coaster

(...) What am I missing or doing wrong here?

Do I shut the unit off until cooling season arrives and heat with baseboards?
Do I turn the baseboards on and put the unit in fan mode for air circulation?
Do I lower the temp setting on the unit even lower?

Any assistance would be appreciated and apologies for the lengthy post.

You may have seen the thread I started a while back http://www.digitalhome.ca/forum/showthread.php?t=42544
I have not been very pleased with the 3.5ton heatpump I got installed in 2006. I just had to have $400 of maintenance done on it (fall 2009) and am still not sure if it is going to make a big difference (looks like it was not configured properly and did not have enough gas; original installer went out of business BTW). It seems to me that heatpumps are only effective between 5 and 15C, that's not a long time in Canada...

[coaster]

My second try at a reply. Got timed out before. Note to self...use Notepad when composing.

"If you've still got baseboards downstairs on, then that heat will rise and the split heat pump doesn't really need to work that hard"

Actually the heat does not rise that well. I'm going to open up the stairwell to help with that.

"So, this is really a supplemental unit which may only affect some (small) percentage of your overall electrical usage."

The unit is located upstairs and, at present, is the only heat source on that level.

"What was your overall usage when you saw the 106 kWh difference?"

1357 kWh compared to the same time period last year at 1251 kWh but 1357 kWh compared to the previous month of 867 kWh. We do not reach the 2000+ mark before December. Our Dec/Jan/Feb last winter average was 2888 kWh per month. I expect by December the inside unit will be nothing more than a means to circulate the warm air provided by the electric baseboards.

"they have overestimated how much savings you'll get from this unit"

A four year, net after grants, payback does seem ambitious even though EfficiencyNB is promoting heatpumps as an option. I'll have to monitor this all winter to see the effect on billing.

[57]

I'm going to open up the stairwell to help with that.

You don't want to do that if you wish to maximize the use of the heat pump, which should be more energy efficient (2-300% heat pump, vs 100% for baseboards)

Edit: I suppose if you have a large enough delta T between upstairs and downstairs (upstairs warmer), then you may be able to "move" some of the heat from upstairs to downstairs, perhaps with additional air circulation.

[txv]

The new mini-splits have inverter drive compressors and are designed to maintain output as the outdoor temperature drops; they are better than their central counterparts in cold climates.

When comparing heating costs, you have to subtract the base load and water use. (many hydro bills include water) Electric water heaters*, stoves, and dryers are large electrical loads and November tends to be mild, so the difference may not be very noticeable until it actually gets cold.

Improper charging reduces efficiency.

Also, you may not realise significant savings if you're heating half the place with baseboards. The mini-split units can have a COP of 3+ above zero, so they're superior to baseboard heaters; keep running it.

*Water heating can consume 500-1000kwh per month alone.

To compare operating costs:

1. Note the electric meter reading

2. Check the meter once a day at the same time, alternate between 100% electric resistance and the heatpump (daily)

3. Subtract each reading from the previous one to calculate kwhs consumed

4. Check an electricity bill which didn't include heating and calculate kwh consumed per day

5. Subtract base load from kwhs consumed between readings

6. Compare the results (electric resistance vs heatpump)

[coaster]

Lots of good input folks. Thanks.

One other question. Is a setting of 66 F too low? I've seen references on web sites about setting the temp so low as to make the unit run inefficiently and thus negate any possible savings.

[littletyler]

Originally Posted by coaster

We own a split-level 1500 sq ft home with electric baseboard heating.We installed a Fujitsu 12RLS mini-split in September 09...

It sounds like your contractor went in the wrong direction when it comes to heating. If your budget just allowed you to install a single zone ductless you should have put it down stairs....
Imagine a 20 story condominium. The tenants on the basement would need ample heat and no cooling in the summer. The tenants on the top floor proiority would be cooling in spring summer. HEAT rises.
Your contractor should have put your single zone system downstairs to eliminate your covection heaters which are always on....

The readon you havnt saved $ is that your upstairs is not hard to heat and those baseboards were never working hard....

Hope this helps

Tlittle

[nascent]

http://604goodguy.com/blog/2013/01/2...-installation/

A UK study found it's not uncommon for heat pumps to achieve less than half of their potential efficiency due to installation factors... If I get one maybe it will just be for the AC, and I'll consider myself lucky if it actually saves a lot of energy.