Air source heat pump and oil boiler

Energysaver

A friend of mine has a standard oil boiler/radiator central heating system. He is proposing to install an air source heat pump in series with the oil boiler feed to the rads. Has anyone come across this type of installation and how did it work out?

baldieman

In our moderate climate the air source may work reasonably well, COP of about 3-4. But on very cold nights the efficiency can drop.
On a negative note, despite all the talk about global warming, there is some evidence that we may be returning to a colder period, so I personally, would'nt be to inclined to go for that heat pump.

Energysaver

Hi baldieman
Thanks for you reply. What sort of temperature would you expect an air source heat pump to get the water up to? I've heard of heat pumps used for underfloor heating systems because they are low temperature, but would an air source pump be able to run a rad system?

Carlow52

Energysaver wrote: »

Hi baldieman
Thanks for you reply. What sort of temperature would you expect an air source heat pump to get the water up to? I've heard of heat pumps used for underfloor heating systems because they are low temperature, but would an air source pump be able to run a rad system?

No because normal rads usually sized or 70 degrees in/50 out ( or similair) : wont get that with heat pump

Energysaver

Carlow52 wrote: »

No because normal rads usually sized or 70 degrees in/50 out ( or similair) : wont get that with heat pump

What if the heat pump were used to preheat the water going thru an oil boiler? Would this work (and reduce oil usage)? When you say that rads have 50 deg C out, is this the temperature that would be returning to the boiler for reheating? If so, is this too high a temp for the heat pump to raise any further? Sorry if these questions are a bit basic.

Carlow52

Energysaver wrote: »

What if the heat pump were used to preheat the water going thru an oil boiler? Would this work (and reduce oil usage)? When you say that rads have 50 deg C out, is this the temperature that would be returning to the boiler for reheating? If so, is this too high a temp for the heat pump to raise any further? Sorry if these questions are a bit basic.

The problem with preheating as u describe is how to stop the oil heated water passing through the heatpump like an extra rad.

You could in theory set up a heat exchanger to do the pre-heat but it would be lots of $$$'s

Re the 50 the basics of rad sizings is extimate the heat requirement for the room, decide on the in/out temp for the water and them size the rad from the brochure.

The higher the in/out, the smaller the rad, the lower the in/out, the bigger the rad, so as a heat pump will get to a max of say 35-40, maybe more ( not my area) retrofitting to rads that were speced for 70/50 will not work. You could size for 40 in/30 out but they would be hugh

Please note that the 70/50 is just to illustrate the point and these vary depending on systems /rads etc.

No prob with what may seem like basic questions: there is too much $$$ at stake not to ask

Energysaver

Thanks Carlow52. What you've said is what I suspected: there needs to be some sort of device (such as a heat exchanger) between the heatpump output and the oil boiler/rad system which would add to the cost. Even in summer you would need the oil boiler to bring the DHW up to temperature, so a solar system may be the more economic option.

Do-more

Both the father in law and the brother in law have replaced their oil boilers with airsource heatpumps in the last 18 months (both live in Sweden) Both have all radiator set ups, no underfloor.

They have the rad valve's set wide open and then rely on room stats for control. Both would be very well insulated houses by Irish standards and the heat output from the rads is fine.

The biggest problem here with airsource heatpumps is the comparatively high relative humidity of our climate. In cold weather this often results in ice forming on the evaporator surface and the energy usage in deicing whacks the hell out of the efficiency.

One solution to overcome this is to install a "earth pipe" so that the incoming air to the heatpump is pre-heated by passing underground, this is relatively inexpensive and will also benefit the overall COP of the system.

I am looking at using this sort of a setup when I get around to building again.

Energysaver

Do-more wrote: »

Both the father in law and the brother in law have replaced their oil boilers with airsource heatpumps in the last 18 months (both live in Sweden) Both have all radiator set ups, no underfloor.

They manage to get enough heat from the pump at swedish winter air temperatures? What size pump are they using and do you know what temperature the rads get up to?

Do-more

Energysaver wrote: »

They manage to get enough heat from the pump at swedish winter air temperatures? What size pump are they using and do you know what temperature the rads get up to?

Yep, air to air and air to water heat pumps are very popular in Sweden, I think they get a water temp. of about 50 deg. C. Not sure what size heat pump but they both have a CTC ECOair link (scroll down page.) I'll be over there for the Christmas and will let you know more details then.

Energysaver

Do-more wrote: »

Yep, air to air and air to water heat pumps are very popular in Sweden, I think they get a water temp. of about 50 deg. C. Not sure what size heat pump but they both have a CTC ECOair link (scroll down page.) I'll be over there for the Christmas and will let you know more details then.

I look forward to finding out more.

Since air source heat pumps seem to work so well at very low temperatures, why aren't they more popular in Ireland? When you consider the cost of laying in the pipes (and associated potential maintenance/repair problems) of ground source heat pumps, I assume that they are probably cheaper than ground source, so what's the catch? Am I missing something?

Do-more

Energysaver wrote: »

I look forward to finding out more.

Since air source heat pumps seem to work so well at very low temperatures, why aren't they more popular in Ireland? When you consider the cost of laying in the pipes (and associated potential maintenance/repair problems) of ground source heat pumps, I assume that they are probably cheaper than ground source, so what's the catch? Am I missing something?

It's all about the humidity/icing problems as far as I can see as with our relatively high ambient temps Air source should work well in theory but the practice shows up the problems.

Here's a prime example.

Earth tubes have been around for a long while but their use in conjunction with air source heat pumps is I think fairly new, the first I learned of it was when I saw it on the "Grand designs" TV show last year.

It would be worthwhile to get the first hand experiance of someone using this kind of set up either here or in the UK.

Jumpy

There is a heat pump in the house I am living in at the moment. It ices up CONSTANTLY. It uses a immersion system to help heat the rads and it hasnt switched off in the time I have been in the house (less than two months) currently using between €10 and €17 euros of electricity a DAY.
Dont go down this route guys, it will cause nothing but heartache and incredible wallet pain.

Do-more

Just to update, FIL has the CTC 105 (5.7kW) heatpump installed in a 165sqM split level bungalow, running costs for the year are approx. €1200. The system is integrated with his existing oil fired boiler. The rads run at between 38 and 45 deg C. The system is set up so that over a 3 hour period if the return water temp. to the heatpump does not hit the setpoint of 38 deg C the oil boiler will fire automatically and continue to fire until the return water temp. has been raised by 5 deg above the temp. at which it started firing.

Even though the house is nearly 30 years old the standard of insulation is very high, triple glazed windows etc. He says the oil boiler fires only very occasionally, and then only when outside temp. is sub-zero. He estimates that he uses less than €100 of oil in the full year. In Sweden the philosophy seems to be to have the heating operating 24 hrs a day keeping the house at a constant 20 deg. the good insulation plays a big part in this.

PoacherWexford

There are some new air source heat pumps arriving onto the market they are High Temperature systems first ones out will be 65 degrees next versions 80 degrees approx. My advice is wait 6 months then search for the high temp versions. Beware of some systems claiming they can work with radiators there are lots of conditions to be met before you can say they actually work. I am aware of two systems that are closely monitored that do work. Even last few days (Jan 09 Kerry) temp on 1 site down to minus 5deg C but lots of work done on insulating house first.

torrestheking

My house, a 2 storey block built 2250sqft with underfloor heating on both floors is consuming approx' 53 units of night rate electricity per day over the last 41 days (This includes heating the water on night rate electricity)

My esb costs for night rate electricity for the last 365 days is €1,307.18, is this high

I only run the heat pump on night rate electricity, 11pm to 8am at present.

Can some one advise me if i should run the heat pump all the time as even though the house is warm all the time, in the evenings when you sit down, it can feel chilly especially at the moment

mick2907

Hi Lads
Just to add a bit of first hand experience on air to water heat pumps. We installed a heat pump just under 3 years ago when we built our house - just under 2500 sq ft and I can only say we were gul-able enough to believe to guy that installed & plumbed our house when he told us that it would only cost us €850 per year to heat our house. Now 3 years later, even though the price of ESB units has gone up over the last 3 years pro-rata our ESB bill never cost us €850 per year to heat. Our ESB costs since we moved in to our new house have doubled from the old house. During the winter months the heat pump costs us on electricty bill between 800 to €1400 every 2 months.
IF I knew then what I know now I would never have touched the heat pump. Oil costs about 3 euro cent per KW heating at the moment a heat pump is costing over 17 euro cent per KW of heating. If anyone wants to see the proof I have all my ESB bills. DONT GO NEAR THE HEAT PUMP UNLESS YOU GET A WRITTEN GUARENTEE ON THE COST OF RUNNING IT.

Borzoi

mick2907 wrote: »

IF I knew then what I know now I would never have touched the heat pump. Oil costs about 3 euro cent per KW heating at the moment a heat pump is costing over 17 euro cent per KW of heating. If anyone wants to see the proof I have all my ESB bills. DONT GO NEAR THE HEAT PUMP UNLESS YOU GET A WRITTEN GUARENTEE ON THE COST OF RUNNING IT.

It sounds like the heat pump is possible under sized or badly set up or both. Get the installer back

Lightning McQue

Mick

What level of insulation did you put into the house and what size and type of heat pump did you instal?

Lightning

BoozyBabe

I would also be very interested in hearing what system you installed, your level of insulation, etc.
We're strongly considering getting one of these, but we're terrified that it doesn't do 'what it says on the tin', & stories like your makes us want to run straight to the tried & tested oil burner.
Considering the system is so much more costly to install than an oil bases system, it'd break my heart to find out afterwards that it turns out to be ridiculously expensive to run also.

Thanks,
BB

gizmo555

Has anyone any experience of the type of air-to-air heat pump which instead of using say, underfloor heating, just blows warm air directly into the house? They effectively work like an air conditioner in reverse.

Seems like they would be a lot cheaper to install, especially for a retrofit, although they would work best in a open plan living space. Anybody know anything, good or bad?

al2009

units working air to air are installed in most office blocks in the country, good insulation is needed and the downside is the air can be drier than with rads. we have 3 installed in our house, good instant heat for those colder bedrooms!

al

Borzoi

gizmo555 wrote: »

Seems like they would be a lot cheaper to install, especially for a retrofit, although they would work best in a open plan living space. Anybody know anything, good or bad?

I've installed one on a retrofit - that used a central outdoor unit, and then the air is distributed by ducts around the building

Costwise I's say it was about the same as Air to water with UFH, from both a running and install cost. The negative aspect would be the bulkheads to hide the ducting (on a retrofit) the amount of nozzles required for air distribution, and the low level noise from the system. Up side is very fast response time, good temperature control, complete cooling system effectively for free.

It could also have included a secondary water coil that would have allowed heater from a back boiler or pellet stove to be used.

gizmo555

Borzoi wrote: »

I've installed one on a retrofit - that used a central outdoor unit, and then the air is distributed by ducts around the building

That's interesting - I'm considering retrofitting a HRV system. I wonder if it's possible to combine both in one system, with the heat pump piggybacking on the HRV ducting. What I had in mind in my previous post was the type of air-to-air system which just blows warm air out at a single location and then relies on ordinary air circulation in the house to distribute the heat.

Would you mind sending me details by PM of your supplier and approximate costs for your setup?

Thanks!

Carlow52

Just be aware that , in general, for many asthma and related illness sufferers, 'blow air' systems are not recommended.

Having said that, good filtration can ease the problem but the positioning of ducts needs careful consideration: its not just 'plug and blow':)

Retro-Fit

You can combine an air to air heat pump in a Mechanical HRV system. It uses the temp difference in the fresh and exhaust air entering and exiting the cross flow heat exchanger. The resultant heat is then added to the circulated air as a post heater with humidifier, giving air at about 21 degrees, moving air at 18 degrees feels cold because of the chill factor of moving air.

You cant overstate though, the importance of continuous insulation, elimination of cold bridge. Most one offs going for planning show little understanding of passive solar design, with winter solar gain and summer shading. Instead of a 50KW boiler, good design a higher spec and quality control on site can enable you to heat the house with a 3.3kw heater in the MHRV which delivers 12kw of heat. low grade heat is best used in combination with air heating rather than with rads or underfloor. It can also be used to cool your home office to make you work better.

If air conditioning is good enough for your car, keeping you at your desired temperature, removing water vapour, and cycling fresh air, why not have something similar in your house. Like a car a house produces most the heat it needs. Simply cut your transmission and ventilation losses and recover a proportion that solar gain, occupant and appliance heat and top up with simple electric to boost a heat pump and you have close to a future proof solution.

The systems need to be SAP appendix Q and Passiv haus accredited.

Borzoi

gizmo555 wrote: »

That's interesting - I'm considering retrofitting a HRV system. I wonder if it's possible to combine both in one system, with the heat pump piggybacking on the HRV ducting. What I had in mind in my previous post was the type of air-to-air system which just blows warm air out at a single location and then relies on ordinary air circulation in the house to distribute the heat.

It would be difficult to combine the two systems due to the very large different air volumes (and hence duct sizes ) used by the two systems

The system I used had a 10" main air supply duct and high velocity air, AFAIK a MHRV typically uses 6-8" duct and lower air speeds.

From what you describe, a standard Air Con heat pump with concealed indoor units would do the job, and use a seperate MHRV

PM sent

al2009

a lossnay unit can bolt directly to a suitable ducted system,providing MHRV and climate control from a single package.

al

Borzoi

al2009 wrote: »

a lossnay unit can bolt directly to a suitable ducted system,providing MHRV and climate control from a single package.

al

True - but it's a not a "suitable ducted system" that I'm talking about, but a high velocity ducted one, for example Unico Sytems http://www.unicosystem.com/

And in general there would be one lossnay (BTW all the major AC co's do similar units) to several indoor ducted units - so the problem can be matching the size, and in a domestic situation, one source of fresh air (the lossnay) is where do you put it?

al2009

i'd be thinking more in the line of a single ducted unit(usually in the attic) ducted to each room, each room has a motorised damper coupled to a temperature controller(airzone), this is what we have done in similar situations.

the unico is also a nice system, have recently commissioned an office installed with this, surprisingly quiet i have to say!!

al

mick2907

Hi Lads
I put in a heat pump 3 years ago that was supposed to run at a cost of €850 per year!!! Never happened even when the cost of Kwh per hour was low. We are now paying up to €2000 to half heat our house with a Dimpco LA 11 heat pump a with under floor downststairs and rads up-stairs, the rads never go past luke warm. We paid €10000 for the heat pump that costs more to run than oil-I have the ESB bills to prove it if anyone wants to see them. Over the last 3 years if we put in oil we would have only spent about 6.5k instead of €14.5k-Big difference. DONT TOUCH THE HEAT PUMP