Oversized rads a good idea?

[wiffola]

Hi all,

We're thinking of replacing our current LPG Vaillant Ecotec 831 boiler and getting an air source heat pump in the next few years - we can't quite afford it at the moment. We want to go for the top of the range Dan Foss.

I could go into deep detail about everything to do with this, but will keep it simple for this thread.

Underfloor heating isn't an option as we have concreted floors downstairs.

The installer has recommended we oversize our 3 downstairs rads by at least 30% and let the heat drift upstairs. All fitted with thermostats. This is something we can do now before we definately decide to get the ASHP.

We have microbore 10-12mm pipework.

My question is: Will oversized rads (30-50%) help or hinder the efficiency of our existing LPG heating setup?

The installer says it will help, as currently a few rads in the house are undersized for the existing system.

My head tells me this is going to increase LPG consumption.

What do you guys think?

 

[DeltaT2]

I wouldn't worry about your radiators too much. I'd worry about your running costs with a ASHP when it hits -14C like it did last winter!!
ASHP work at there optimum with a outside temperature of >8C and a system with a mean water temperature <50C don't let anyone tell you anything else.

Keep your LPG boiler for the cold cold winter days. There's lots of smoke & mirrors with ASHPs!!

 

[Agile]

Putting in larger rads will enable your boiler to condense more and be a little more efficient.

You could also do this by reducing the boiler flow temperature but few bother to do that.

Of course you could have that done automatically by fitting weather compensation and for the cost of that its something you should definately do.

You seem to have a lot of money to spend! Have you calculated what you expect to save with ASHP ? It would probably take 20 years to recover the capital cost. During that time it would probably break down and need to be replaced!

Tony

 

[wiffola]

Thanks Both.

There seems to be a lot of negativity towards ASHP. Which is concerning.

I don't have lots of money to spend but I don't mind putting my savings into investments for the future. We've just put a 2kw PV array on the roof for instance.

I had the money for those, so thought, best to do it now while the FIT is at it's highest.

I kind of see ASHP in the same way. Yes they may have a long payback (could be quicker with RHI) but it's more of a safe guard for the future. LPG is already insanely expensive and it's just going to go up and up. Electricity is too but at least it's renewable and available wherever you live.

Any thoughts on this?

You could also do this by reducing the boiler flow temperature but few bother to do that.

Of course you could have that done automatically by fitting weather compensation and for the cost of that its something you should definately do.

When you say flow temp, are you refering to the rad temp on the boiler? If so, we have this set very low at the mo 50 degrees whatever the weather - which is chilly but bearable. How would you recommend running the boiler for optimum efficiency?

i've never heard of a weather compensation device...what and how does that work?

Thanks for eveyones help.

 

[DeltaT2]

Over the last two Winters; ASHPs have cost a fortune to run. We're taking another one out next week! The guy we are removing it for said it was useless in cold weather & cost a fortune to run. He also told me the Feed-In-Tariff will not happen for ASHPs.

Weather compensation; monitors the outdoor temperature, indoor temperature, the Return water temperature to the boiler & regulates the boiler according to the heat demand.

 

[JohnD]

the bigger rads will also heat the house faster, e.g. when you have been out all day, or been away, and will give extra capacity to deal with exceptionally cold weather. In most cases, modern boilers have a max power that is a lot greater than calculated heat loss of the house, so they seldom run flat out.

Provided you have good temperature control from a room stat and TRVs, they will not use extra fuel as they will turn off once the room iswarm.

 

[Agile]

The latest ASHPS are quite efficient down to about -10 C.

The problem is that the capital cost is very high. We dont have enough experience of how long they will last for. I would be surprised if it averages more than 10 years though.

An ASHP may well be a heat source to consider with a new installation. But you already have a a newish boiler. It would take a long time to recover the extra cost of an ASHP compared wiut a gas boiler even if fed by LPG.

A solar hot water installation might be more worth considering.

Your boiler is already very efficient if you can manage with a flow temp below 60C and hardly worth adding rad output. But you have fallen into the trap of being sold the idea of replacing with larger rads. Its more cost effective to ADD new rads!

Electricity being renewable? The last I heard was that less than 2% is in the UK.

Tony

 

[Hufty]

Would strongly recommend a weather compensating controller and in your case with an ecoTEC it would be a Vaillant VRC430 controller (or the wireless VRC430f). Then radiator size is not such an issue.

Quick comment on ASHPs: don't know much about them myself but having toured Norway this summer, can tell you that loads of people have either got aircon or an ASHP bolted onto their house. Given that it was cold in June, I'm guessing it wasn't aircon.

 

[Agile]

I think that you will find that Norway has a high proportion of hydro power which is much cheaper to buy than our electricity based on using fossil fuels.

Not only does it meet the renewables argument but it will be likely to be the cheapest power source.

Tony

ConsumptionOf the total production in 2007 of 137 TWh, 135 TWh was from hydroelectric plants, 1 536 GWh was from thermal power, and 892 GWh was wind generated.[1] In same year, the total consumption was 115 TWh.[2]

The annual electricity consumption was about 26-27 GWh per inhabitant during 2004-2009 when he European union (EU15) average in 2008 was 7.4 GWh. Norway’s consumption of electricity was over three times higher pro person compared to the EU 15 average in 2008. The domestic electricity supply promotes use of electricity.

 

[Hufty]

When you say flow temp, are you refering to the rad temp on the boiler? If so, we have this set very low at the mo 50 degrees whatever the weather - which is chilly but bearable.

As low as possible without it being chilly. 50deg flow seems a bit hair-shirt, but it depends on your house insulation levels - lag your lagging! As a rule to get the boiler to condense you want the return water from the rads to be below 57degC. Your system might lose 10-20degrees through the radiators, so a flow temp of 65-75deg wouldn't be reckless if it's cold outside. If you RTFM on the Vaillant, d40 and d41 in the diagnostics tell you the flow and return temperatures (or vice versa). You only have to press [+] and on the front panel to get to the diagnostics - it's safe to do.

In spring you might turn the boiler down, in the depths of winter turn it up. Weather compensation does all this for you automatically.

 

[Hufty]

I think that you will find that Norway has a high proportion of hydro power which is much cheaper to buy than our electricity based on using fossil fuels.

Not only does it meet the renewables argument but it will be likely to be the cheapest power source.

Nothing in Norway is cheap. I don't think they use gas much if at all, so everything is either electricity or wood. I mentioned it because it's consistently colder than here yet loads of people seem to have gone for ASHPs, so they probably work fine.

Over and Out

 

[wiffola]

Would strongly recommend a weather compensating controller and in your case with an ecoTEC it would be a Vaillant VRC430 controller (or the wireless VRC430f). Then radiator size is not such an issue.

Quick comment on ASHPs: don't know much about them myself but having toured Norway this summer, can tell you that loads of people have either got aircon or an ASHP bolted onto their house. Given that it was cold in June, I'm guessing it wasn't aircon.

Thanks Hufty.

We currently have an old looking wired thermostat (left by previous owners) and we bought a timeSWITCH 140 a year ago.

The wireless VRC430f sounds like a good idea - i can install it myself and put the thermostat in a better location too. Currently its close to an external door so would benefit from being in the main living area.

Will this render my timeSWITCH 140 pointless?

 

[DeltaT2]

We pay much, much more for our leccy and a lot less for our Nat gas - which is bought in bulk from places like Norway!! Here in Scotland we have loads of hydro & wind, and still pay a fortune for leccy - cause we're part of the UK national grid.
The used car salesmen can tell you that their ASHP has a COP of 4+, they lie, it hasn't. Your leccy is expensive, so regardless of the COP, if the leccy is expensive & it's -14C, it'll cost you serious money to run.

Buy a cheap ASHP if you're a serious tree hugger, twin it with your LPG boiler, upgrade your LPG boiler controls, use your ASHP until it gets very cold.............Job done!!
That'll be £1K consultancy fee please!!

Lovely country Norway & lovely people.

 

[David937]

It will replace the Timeswitch yes, all you do is unplug the Timeswitch and plug in the VRC430f's transmitter to the boiler fascia, you only need to wall mount the transmitter if you don't get good signal quality with it mounted on the fascia.

Wall mount the actual VRC430f in the main living area and remove the TRV on the radiator there OR set it to max.

It will offer a lot more flexibility with your heating, e.g. you can choose different temperatures for different times of the day.

 

[dcawkwell]

Forget Dan Foss.
Overpriced like most of the offerings from many of the air source heat pump suppliers at the moment.
Most of the air source heat pumps are very similar inside.

Search a little harder on ebay for example and you'll find some more reasonably priced units approx £1200 for a 12kw one.

To see how your current radiators perform turn your current boiler down to about 50 degrees. If they manage to heat the house successfully then you are ok.
I would suggest a buffer tank for the air source heat pump that is heated by an air source heat pump and the current lpg boiler as backup and booster.

The lpg boiler would only cut in if the air source heat pump isn't keeping up with the heat demand.