Heat pumps in Maine: Set it and forget it? Or turn it off for the winter?

Comment

Comment by Willem Post on November 4, 2018 at 9:41am

Heat Pump Performance:The heat pump COP on MFR data sheets is for test operation at a source temperature of 47F.

That temperature is per industry standard.

Heat pumps from Japan are well-designed, reliable, high tech systems.

They work well in houses that are highly insulated and sealed, such as with R-6 to R-9 triple glazing, R-5 to R-10 insulated doors, R-40 walls, R-20 basement, R-60 roof, 85% efficient heat recovery ventilator, open floor plan, preferably all on one floor.

The glowing media reports about heat pumps, often written by lay reporters, usually involve such houses.

Such houses have long time constants; slow to warm up, slow to cool down.

You may want to look up the PassivHaus standard, which has been around for  at least 30 years.

 

The COP of a heat pump decreases when the source temperature decreases, say to 0 F.

This happens on colder days in winter when heating requirements are higher.

Owners find they cannot heat their houses, so they turn on their traditional furnace, or wood stove.

That means their heat pumps operate mostly during moderately cool days.

Under those conditions the opportunities for annual savings are minimal.

 

Overhyping Heat Pumps:Efficiency Vermont, VPIRG, etc., have been shamelessly overhyping heat pumps. 

VPIRG, a lobby organization, booster of renewable energy, mostly financed by Vermont RE businesses, estimated the annual savings at $1000 to $1500 per year on a $3000 household-heating bill.   

EV provides subsidies, and EV-qualified contractors charge a little more because of the subsidies.

 

People Complaining About Less than Promised Savings: It is likely many heat pumps were installed in houses with average insulation and sealing. It is likely people complained to their legislators, etc., about less than promised savings. As a result the VT-DPS made a survey and wrote a report, and found averageannual savings were $200/y (for a $4500 installation that will last about 15 years, not counting any costs for service plans and maintenance.

 

From the VT-DPS report:

 

1. Overall dollar savings are impacted by the efficiency of the back‐up fossil fuel system. The higher the efficiency of the back-up system, the smaller the amount of fuel is being displaced by the heat pump. 
2. Houses with poor insulation levels and air leaks will not get as much benefit out of a heat pump, as will highly sealed, well- insulated houses. 
3. It is unlikely a heat pump by itself would be sufficient to heat a typical house, without use of a traditional heating system as a backup on cold days. 

http://publicservice.vermont.gov/sites/dps/files/documents/Energy_E...

 

NOTE:For the annual savings to average only $200/y, most of the houses had to have poor insulation and sealing. EV and its approved contractors likely did not properly survey those houses and did not give proper warning to those households. They likely were eager to install as many heat pumps as possible.

Comment by Willem Post on November 4, 2018 at 9:41am

The ratedCOP of a heat pump is the energy out/energy inputat a source temperature of 47 F.

The rated COP is determined under test conditions in a laboratory

 

The averageCOP is less at lower than rated outputs, and due to on/off cycling, and as source temperature decreases, i.e., the heat pump output decreases as it get colder. That perversity happens when the heating load of a building is increasing!

 

In the real world, the heating load of a building increases exponentially as it gets colder, i.e., it is not linearly increasing, but with an exponent greater than 1, say 1.2

 

Owners know their heat pumps are working hard, because fans are at high speed, it is cold outside, say 0 F, the COP decreases to 1.2 to 1.4, but they do not get enough heat their buildings.

 

Owners may run under such conditions more hours than they should.

Efficiency Maine recommends owners to “set it and forget it”. That surely is the most stupid notion of the year.

A better approach is to turn off the heat pump and use onlythe traditional furnace, or wood stove on colder days

All that leads to little savings.

 

Houses Built to the Passivhaus Standard

Such houses, with the heating system off, take at least a day to cool down 1 to 2 degree F on cold days in winter, because of internal heat generation by people, lighting and appliances, food heating, solar gain. 

A 2000 sq ft house would require only a resistance heater of about a 1.5 to 2.0 kW to maintain temperature and heat domestic hot water.

 

NOTE:A standard fuel oil furnace may be rated at 85% efficiency, but the seasonal average efficiency likely would be about 70%, because of the system loosing heat up the chimney after it shuts down, and due to having to warm up again after it starts up, just as with a car.

Comment by Penny Gray on October 31, 2018 at 6:22pm

I've thought about installing one of these heat pumps in my mom's house (she lives in Freeport) but up here in far northern Maine, I can't even bear going to my friend's house in winter anymore because she has a heat pump.  Her house is always clammy cold unless she breaks down and lights a fire in her wood stove.  So I'd say they have their limitations.  I love the idea of geothermal, but that's WAY out of my price range, so I rely on a giant wood stove made from truck tire rims, with a huge custom made cast iron heat converter on the top.  Right now it's cranking away, my house is cozy and it's snowing outside. 

Comment by Willem Post on October 31, 2018 at 12:05pm

Eric,

Please read this article

http://www.windtaskforce.org/profiles/blogs/heat-pumps-oversold-by-...

Comment by Eric A. Tuttle on October 31, 2018 at 1:15am

I am not sure how Efficiency Maine has selected Contractors, in the past or currently. However, I can attest to the fact that within the climate zone (of which Maine has many microclimates) in Abbot Maine the electricity bill went up considerably, while the Oil bill went down for my 84 year old friends trailer that has been remodeled as a home. 

I would call it a draw on heating, just 12 miles north of the 45th parallel in Central Maine, but would call it a Positive on the AC side of the function of these devices which reduced the summer electric bill in comparison to a 120v 20k BTU unit. 240v units may have been a draw also. 

Though I am still leary, I am considering replacing an ALL electric heated home with one of these units as Electric heat is still by far at least double of Oil heat and Oil fired Hot Water.

Since I do not have the land, I will have to do at least one Air Heat pump system, but would recommend thermal (wells or septic style collection of constant 54 degree temp vs -30 at times Air.

Comment by Willem Post on October 30, 2018 at 8:50pm

Efficiency Maine and its approved contractors have been hyping heat pumps and installing them in houses that are poorly insulated and sealed.

Such houses lose a lot of heat in winter and cannot be kept warm with heat pumps, which have low heat outputs at low outdoor temperatures.

Set it and forget it in winter is the most ridiculous notion I have heard.

It is much better to turn them off on cold days, and run the regular furnace instead.

Use the heat pump only when temps are moderately cold.

Now if you are one of the very lucky few who has a highly sealed, highly insulated house, it is likely you will be able to heat your house with a heat pump, if it has an open floor plan 

You may need electric space heaters for each of the bedrooms, so they stay above 55F to avoid condensation inside walls.

Comment by Penny Gray on October 29, 2018 at 6:43pm

I can vouch for the fact they don't work in winter.  I don't have one but I have two friends that do and they are virtually useless when it gets cold.