Heat Pump

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shawcroft
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Heat Pump

Post by shawcroft » Wed Sep 25, 2013 9:58 pm

A question on heat pumps..
Our younger son is thinking about purchasing a small condo in the Washington DC area. Many of the building he has seen are old, some 80-100 years, and have been converted into 1-2 bedroom residential units for sale. Although most of the apartments/condo units he has seen during open houses are 80 or so years old, they appear to be well-built.
One which is about 90 years old is described as being cooled by a heat pump- and, indeed, exterior photos of the 4 story building do not show any window air-conditioners while the buildings next door (of about the same vintage) both show folks with room air-conditioning units hanging out the windows.
I guess I am surprised this type of improvement could be done in a building of that vintage. How good are heat pumps as a means of cooling a building?
Washington DC can have brutal summer weather...
Shawcroft

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LadyGeek
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Re: Heat Pump

Post by LadyGeek » Wed Sep 25, 2013 10:07 pm

This thread is now in the Personal Consumer Issues forum (heat pump).
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sunnyday
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Re: Heat Pump

Post by sunnyday » Wed Sep 25, 2013 10:12 pm

I live in NC and have a heat pump. It's terrific at cooling. My bigger concern in DC would be the heating aspect. When the temperature drops below 40 they typically need auxiliary (inefficient electric) heat. My electric bill in the winter is significantly more in the winter than summer. I would think the difference would be even greater in DC

2comma
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Re: Heat Pump

Post by 2comma » Thu Sep 26, 2013 12:12 am

I agree with sunnyday, your son will be fine with the cooling (assuming properly sized unit with good ductwork...). Heating will be an issue if the home doesn't have a furnace. Heat pumps are not as capable at producing heat so electric heat strips are used to help. The heat from a heat pump is not as hot as a furnace so many people don't feel as toastie in the winter. Here is a link to the Carrier website with some information and additional links: http://www.residential.carrier.com/know ... orac.shtml

With all of that said I'd prefer the heat pump over several window units any day! I'd check on the age of the HP; if it's over 12 years old it's beginning to approach it's end of life.
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Valuethinker
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Re: Heat Pump

Post by Valuethinker » Thu Sep 26, 2013 3:20 am

Just on the physics of the thing, a Heat Pump is effectively a super sized room air conditioner (Air Source Heat Pump as opposed to Ground Source/ Geothermal).

In the summer it does what an AC does. In the winter it reverses direction and acts like a fridge, 'cooling' the outside air and putting the heat out through a heater coil (which happens to be inside the house).

It's a very common form of heating/ AC in the South, so it could handle Washington DC summers well. On heating, the number I had heard was below about 20F the electric bar kicks in-- interesting that the other poster has a much higher number (40s). Either due to an older HP OR the manufacturers are not telling the full truth (shock, horror ;-)).

There are a couple of measures of efficiency but one is Coefficient of Performance (kwhr of electricity burned to move kwhr of heat or 'coolth'). And ASHP should average around 3.0 ie uses 1/3rd electricity to get 1 unit of heat (although the measure used for Air Conditioning is something called Seasonal Energy Efficiency Ratio or SEER -- wikipedia has an explanation. I think 12 is now the minimum allowed, 15 is good (about 1/4 more efficient)). COP falls as the gap between internal temperature and outside gets bigger-- electric bar heat, by definition, has COP of 1.0.

When replacing, it is worth getting Energy Star (in AC terms, a SEER of 15 say). Electricity prices are not low, and this is something that is only replaced every 10-20 years.

http://www.energystar.gov/index.cfm?fus ... gw_code=EP

there is a calculator on the rhs (excel spreadsheet).

hectorochoa
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Re: Heat Pump

Post by hectorochoa » Thu Sep 26, 2013 5:05 am

Agree with others...I live in Georgia and a heat pump is how houses are cooled here (as well as heat them in the winter). Heat pump works great for air conditioning, but it would not be adequate to heat in the winter in DC, as it barely does the job in GA.

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Frugal Al
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Re: Heat Pump

Post by Frugal Al » Thu Sep 26, 2013 8:16 am

In the DC area an air source heat pump would work fine. DC actually has a fairly mild climate. Proper sizing of the unit is important, as well as proper insulation of the building to be heated and cooled. Many people don't like heat pumps because the heating air flow is cooler than other types of heating units. Because of the cooler air flow, without proper insulation a heat pump can have a difficult time getting a space to temperature without triggering supplemental heat.

Valuethinker
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Re: Heat Pump

Post by Valuethinker » Thu Sep 26, 2013 8:25 am

Frugal Al wrote:In the DC area an air source heat pump would work fine. DC actually has a fairly mild climate. Proper sizing of the unit is important, as well as proper insulation of the building to be heated and cooled. Many people don't like heat pumps because the heating air flow is cooler than other types of heating units. Because of the cooler air flow, without proper insulation a heat pump can have a difficult time getting a space to temperature without triggering supplemental heat.
Winter temperatures here in the UK are generally around 30F (depending where) to 40F. So HPs are an option, as yet little used. People heat with oil or LPG instead.

The trick with a HP here is that the house has to be well insulated: then you run the HP virtually *all* the time, because its heat output (sorry Centigrade) is 45C (113F) whereas rad hot water output is usually around 70C (158F).

The COP of a HP falls with the increasing difference between input and output temperature.

The UK usual is a not well insulated house and then a massive gas boiler (heats both hot water and the radiators) which you only yank on when you come home or get up-- house heats and cools rapidly. Studies show new HP users don't understand that well and use the systems incorrectly.

For HPs to work well, you need a well insulated home because the heat output is so much lower (lower temp).

To beat your gas price, for heating, your HP needs to be running a COP of c. 3.0 (1 kwhr from electric co costs c. 3-4 kwhr from gas company, and assuming a 90% efficiency gas furnace).

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deanbrew
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Re: Heat Pump

Post by deanbrew » Thu Sep 26, 2013 8:33 am

I'm going back quite a few years, but I had a townhouse in the DC are that was heated and cooled with a heat pump. DC has a pretty moderate climate. Certainly colder than NC, but it doesn't typically stay cold long in DC, even in winter. I remember the resistance heat coming on fairly infrequently, and only when the temp outside got colder than 30 degrees or so. My utility bills were fairly even in the winter and summer, and lower, of course in the spring and fall.

One recommendation: get a programmable thermostat made specially for a heat pump. Heat pump thermostats raise the heat gradually in the morning, allowing the space to heat up gradually with "heat pump" heat, not resistance heat. If you use a thermostat made for a gas or oil furnace, it will go up the full amount in the morning and trigger the high-cost resistance heat. If you don't use a programmable thermostat, just leave the thermostat at one setting. The worst thing you can do (in terms of operating cost) with a heat pump is move the thermostat up and down manually. When heating, heat pumps work by blowing air that is 85-100 degrees, which feels cool to the skin (the reason many people complain about heat pumps blowing "cold air"), but nonetheless warm a room up, albeit very slowly.
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sunnyday
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Re: Heat Pump

Post by sunnyday » Thu Sep 26, 2013 9:09 am

For other heat pump owners, at what temperature does your auxiliary heat kick in?
Valuethinker wrote: It's a very common form of heating/ AC in the South, so it could handle Washington DC summers well. On heating, the number I had heard was below about 20F the electric bar kicks in-- interesting that the other poster has a much higher number (40s). Either due to an older HP OR the manufacturers are not telling the full truth (shock, horror ;-)).
Maybe the new ones are more efficient, but I've always heard the number is higher than 20 degrees. My HP is 7 years old. I know when the Aux heat kicks in because the light on the thermostat goes on and the heat produced is noticeable hotter. It hardly ever gets down to 20 here, but is in the 30's quite a bit

Valuethinker
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Re: Heat Pump

Post by Valuethinker » Thu Sep 26, 2013 9:38 am

sunnyday wrote:For other heat pump owners, at what temperature does your auxiliary heat kick in?
Valuethinker wrote: It's a very common form of heating/ AC in the South, so it could handle Washington DC summers well. On heating, the number I had heard was below about 20F the electric bar kicks in-- interesting that the other poster has a much higher number (40s). Either due to an older HP OR the manufacturers are not telling the full truth (shock, horror ;-)).
Maybe the new ones are more efficient, but I've always heard the number is higher than 20 degrees. My HP is 7 years old. I know when the Aux heat kicks in because the light on the thermostat goes on and the heat produced is noticeable hotter. It hardly ever gets down to 20 here, but is in the 30's quite a bit
7 years isn't enough to make a difference I don't think. I don't think that HPs have had leaps that big in technology (except maybe on the control side).

What Deanbrew says is relevant, perhaps? I wouldn't have thought of that (although it's obvious if I think about it) that a thermostat which doesn't understand the thermal characteristics of your house (the ideal HP house is highly insulated, and the HP comes on hours before you get up in the morning or come home in the evening) then it will tend to default to bar heating ie try to warm up too fast.

Thank you for your input which is very interesting-- I had too low an estimate of the temperature at which the HP auxiliary heat comes on. In Ontario, if people have HPs, they tend to be ground source ('geothermal').

azb
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Re: Heat Pump

Post by azb » Thu Sep 26, 2013 12:43 pm

We have a heat pump that is set to work at temperatures down to 32 degress in the winter. We have a furnace that kicks it for colder temperatures. We live in the Dc area and the heat pump does the vast majority of the heating in the winter.

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xplorer
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Re: Heat Pump

Post by xplorer » Thu Sep 26, 2013 1:17 pm

We are in the DC area heating and cooling a little over 2,800 sq ft with a heat pump rated at SEER 15 (Ruud). We have an all electric home. AC works great with highest bill running $220 per month. This has occurred only once in 4 years since the unit went in. Heating is very good with highest bill $190 per month, only a couple times in the same period. By comparison, our off season bills are around $90. This is a two-stage compressor system with variable speed fan so it runs a fair amount of the time during the summer and winter in the lower setting. When the kids are around for holidays its running at high trying to keep up with the doors opening and closing. It took us a season or two to become accustom to a heat pump 'pumping a lot' -- we came from the mid west with natural gas and 'hot' heat.

p14175
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Re: Heat Pump

Post by p14175 » Thu Sep 26, 2013 5:13 pm

Ductless mini split heat pump systems are a great way to retrofit an older building. Maybe that's what they used.
http://energy.gov/energysaver/articles/ ... heat-pumps

Randomize
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Re: Heat Pump

Post by Randomize » Thu Sep 26, 2013 5:28 pm

p14175 wrote:Ductless mini split heat pump systems are a great way to retrofit an older building. Maybe that's what they used.
http://energy.gov/energysaver/articles/ ... heat-pumps
The ductless models tend to be more effective at heating than their ducted counterparts for whatever reason. The temperature in my area hovers between 0 and 20F for a couple months out of the year and my ductless heat pump has had no issues keeping up.

For those of you who own a regular heat pump, there's a thermostat on the unit that dictates when the backup furnace will kick on. Some of them are adjustable (but all of them can be replaced) if you're interested in lowering the threshold a few degrees and saving some money. The contractors that work for my company actually made kind of a stink about us asking them to set the thermostats lower because the cheapest ones aren't adjustable and are set at the highest level allowed by code. Maybe you got lucky and your contractor didn't want to save money but odds are yours is one of the cheap ones. The price difference was something like $15 bucks for the ones with a lower threshold vs. $5 bucks for the ones with the higher threshold.

SamB
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Re: Heat Pump

Post by SamB » Fri Sep 27, 2013 3:30 pm

I live just outside of DC and use a heat pump to heat and cool a four bedroom home. I replaced the old heat pump with a new one about three years ago. The new unit has a variable speed fan, which is very good at increasing efficiency and overall comfort. My unit has only a single stage compressor, and there might be additional efficiency with a multistage unit, but there is the usual cost/reliability trade off.

I have never had a problem with adequate heating or cooling. Of course if you need instant satisfaction, and like 80 degree plus temperatures in the dead of winter and 68 degrees in the middle of the summer, then you should look at gas and a regular AC unit.

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Re: Heat Pump

Post by technovelist » Fri Sep 27, 2013 3:37 pm

We have a geothermal heat pump and it keeps our normally insulated 2000 sf house nice and cool in the Texas summer except for the very hottest (110+ F) days, when it can't get it much below 80. Our bills are rarely more than $130/mo. in the summer.

It usually doesn't get very cold here in the winter; I think the lowest temperature we've seen in 15 years is 9 degrees, and that happened only once. We usually use wood heat when it's really cold, but the heat pump can keep it at 68 or so even when it's that cold outside.
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scubadiver
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Re: Heat Pump

Post by scubadiver » Fri Sep 27, 2013 8:29 pm

shawcroft wrote:A question on heat pumps..
Our younger son is thinking about purchasing a small condo in the Washington DC area. Many of the building he has seen are old, some 80-100 years, and have been converted into 1-2 bedroom residential units for sale. Although most of the apartments/condo units he has seen during open houses are 80 or so years old, they appear to be well-built.
One which is about 90 years old is described as being cooled by a heat pump- and, indeed, exterior photos of the 4 story building do not show any window air-conditioners while the buildings next door (of about the same vintage) both show folks with room air-conditioning units hanging out the windows.
I guess I am surprised this type of improvement could be done in a building of that vintage. How good are heat pumps as a means of cooling a building?
Washington DC can have brutal summer weather...
Shawcroft
We live in Northern VA and have a heat pump / AC unit for a single family home. Being from upstate New York originally, I'm of the opinion that DC doesn't actually have a winter, just a really long fall that eventually becomes spring. We just replaced our 21 year old unit in April and have noticed a fair reduction in our utility bills (admittedly, some of that is probably due to the mild summer we had). Our highest electric bill last winter was $262 and we kept the heat between 68 and 70 most of the time. EDIT: Barring an unusually cold winter, I'm not expecting to see anything close to $262 this year.

Heat pumps are very common around here, particularly in areas where there are no natural gas lines. Assuming the condo is well insulated, I would think that a heat pump would be fine, even if you do use the electric heat from time to time. Remeber, the electric portion just supplements the heat pump when it's too cold. Most of the time the heat pump itself will be effective.
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Randomize
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Re: Heat Pump

Post by Randomize » Thu Dec 12, 2013 11:57 am

Heat pumps actually have a built-in thermostat that determines when the backup resistance heat kicks in. The cheapest ones (less than $5 dollars) are set to 40 degrees so contractors will frequently use them even though the units can efficiently operate at lower temperatures. Do yourself a favor and spend the $10 bucks on a 30 or 35 degree thermostat and install it yourself.

Yes, many contractors are more interested in saving themselves $5 bucks in installation costs than they are in the hundred of dollars in savings a different thermostat would save you. My job is in energy efficiency and you wouldn't believe the pushback we got from them when we tried to change the local code to require the more expensive thermostats.

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Re: Heat Pump

Post by SteveNet » Thu Dec 12, 2013 12:24 pm

technovelist wrote:We have a geothermal heat pump and it keeps our normally insulated 2000 sf house nice and cool in the Texas summer except for the very hottest (110+ F) days, when it can't get it much below 80. Our bills are rarely more than $130/mo. in the summer.

It usually doesn't get very cold here in the winter; I think the lowest temperature we've seen in 15 years is 9 degrees, and that happened only once. We usually use wood heat when it's really cold, but the heat pump can keep it at 68 or so even when it's that cold outside.
I had a geothermal installed as well about 3 yrs ago to replace my traditional air source Heat pump. We chose the well method for the fields here in Tennessee.
All a Heat pump is is an Air conditioner that can run in reverse. So for cooling it's the same as a regular air conditioner.
The Geothermal (ground source) doesn't care how hot it is outside or how cold it is. As it's always around 56deg 300ft below the surface of the ground. cop around 5.
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