ASHP - Wet system

[ArgyllMC]

Hi,
Having spoken with 3 different plumbers and got 3 totally different answers I have decided I had better try to get some impartial advice before proceeding down the wrong path!

I have just moved into a nice 1970's bungalow. Having spent all summer insulating the place I now have a nice insulated box and the plan is to remove the baxi gas back boiler heating system (it runs off 47kg bottles at an alarming rate) and fit an ASHP system coupled to a wet system, providing domestic hot water and heating.

Obviously this system runs at low temperatures so all the emitters have to be replaced with larger more efficent units, the plan is to use the Myson double panel Type 22g emitters. I have done all the calcs for each room and have specified the emitters. My troubles start when trying to get each plumber to spec the pipe sizes they would run the system in, flow rate is more critical as I understand due to the low temperatures involved.

The most sensible system seemed to be running a 22mm pipe to a central manifold before running seperate legs to each emitter at 15mm. Each emitter would have a thermostatic valve fitted apart from the hall which would form the bypass circuit. This was in speedfit plastic. Longest pipe run would be 34m (combined flow and return including run between manifold and hydro box)

What do people rekon? From what I have read the pipes are capable of carrying the heat capacity however, speedfit internal bore is dramatically restircted at each joint surely the flow therefore would be insufficent?

Thanks for reading this far!

Mark.

 

[Agile]

Why do you think that speedfit is dramatically reduced?

Have you ever looked at the inside of a rad valve?

Have you done fuel cost calcs to compare the different costs?

Its quite likely an ASHP will be comparable as you dont have NG and can only choose oil, LPG or off peak electricity as alternatives. Usually oil is the cheapest both to install and run.

Part of the problem is that heat pump performance is not well documented and makers claims are usually very over rated.

Worse when its cold outside the performance usually falls off severely. The makers and installers dont want to discuss that!

Tony

 

[ArgyllMC]

Thanks Tony, I am very interested in your points of view.

I appreciate valves etc are restricted, I was just comparing a joint in copper pipe to that in speedfit, the internal sleeve reduces the internal diameter and therefore restricts flow? I can't find anything documenting flow characteristics for speedfit.

I have looked fairly in depth at fuel costs, oil was cheaper however I plan to be in this house for 15-20 years so the chances of oil still being cheaper to run even in 5 years time is questionable. Gas is in the same boat.

The question of installation costs is also rather more complex. The heating system is a real mess with the now fitted gas system having been fitted in the 80's to replace the original coal fired baxi system. Additional radiators have been fitted adhoc over the years and as a result I have a mixture of microbore and 15mm piping with very old an inefficent emitters so no matter what system the piping and rads have to be replaced!

I have done a lot of research into the pro's and con's of the ASHP systems. Locally I know of a lot of units the same as I am looking to fit which came through last winter o.k. keeping houses warm although they were using underfloor heating rather than radiators.

Perhaps I am being to pedantic and should just let the plumbers get on with it I just like to check things out a little before commissioning work.

 

[D_Hailsham]

Obviously this system runs at low temperatures so all the emitters have to be replaced with larger more efficient units

The efficiency of a radiator is always 100%. Yes, you will have to oversize them as the output of a radiator depends on the flow, return and room temperatures.

I have done all the calcs for each room and have specified the emitters.

How did you work out how much the rads needed to be oversized?

My troubles start when trying to get each plumber to spec the pipe sizes they would run the system in, flow rate is more critical as I understand due to the low temperatures involved.

The temperature differential (flow-return) is the determining factor. The greater the differential, the lower the flow rate, so the pipe can be a smaller bore.

The most sensible system seemed to be running a 22mm pipe to a central manifold before running seperate legs to each emitter at 15mm. Each emitter would have a thermostatic valve fitted apart from the hall which would form the bypass circuit.

You may not need 15mm, it will all depend on the size of each radiator. Do you have a layout diagram you can post, showing location and size of rads etc and the other design data?

From what I have read the pipes are capable of carrying the heat capacity

I should hope so!

speedfit internal bore is dramatically restricted at each joint surely the flow therefore would be insufficient?

This will affect the size and setting of the pump required to give the correct flow.

Although intended for copper pipe installations, you should read Small Bore Heating Systems and Copper Tubes in Domestic Heating Systems. The same principles apply to plastic piping as well.

 

[Norcon]

The efficiency of a radiator is always 100%

Not if their covered over with clothes as many people do or sludged up inside with gunk.

 

[D_Hailsham]

The efficiency of a radiator is always 100%

Not if their covered over with clothes as many people do

That's not a fault of the radiator and the efficiency will not alter.

or sludged up inside with gunk.

The radiator may not give off the same amount of heat but the efficiency will still be the same.

Efficiency is defined as output ÷ input. If the rad is covered/sludged, both will decrease by the same proportion.

 

[ArgyllMC]

Thanks for your thoughts I have a sketch on my desk of the layout which I will post tomorrow. Below I have answered your other questions, fingers crossed I have grasped it right!

I have done all the calcs for each room and have specified the emitters.

How did you work out how much the rads needed to be oversized?

I used the figures from the engineer who is going to supply the Diakin heat pump system along with the calculations from Myson to work out the heater output. see method below.

Required room temperature is 20 degrees, mean water temperature in heating system will be 50 degrees therefore temperature differential = 30 degress. From the chart in Mysons technical info for panel emitters this differential gives a correction factor of 0.51. So the lounge requires 2267 watts of heat after applying the correction factor I actually need emitters rated at a conventional output of 4445 watts to give the required output at the mean system temperature of 50 degrees.

My troubles start when trying to get each plumber to spec the pipe sizes they would run the system in, flow rate is more critical as I understand due to the low temperatures involved.

The temperature differential (flow-return) is the determining factor. The greater the differential, the lower the flow rate, so the pipe can be a smaller bore.

The most sensible system seemed to be running a 22mm pipe to a central manifold before running seperate legs to each emitter at 15mm. Each emitter would have a thermostatic valve fitted apart from the hall which would form the bypass circuit.

You may not need 15mm, it will all depend on the size of each radiator. Do you have a layout diagram you can post, showing location and size of rads etc and the other design data?

I will post a sketch in the morning.

From what I have read the pipes are capable of carrying the heat capacity

I should hope so!

Mmm I am not a plumber only checking what I have been told!

speedfit internal bore is dramatically restricted at each joint surely the flow therefore would be insufficient?

This will affect the size and setting of the pump required to give the correct flow.

The Diakin hydro box comes with pump included so as I read it I only have one choice and as such the flow will need to be within the capability. minimum flow rate 12l/min nominal flow rate 24.1l/min

Although intended for copper pipe installations, you should read Small Bore Heating Systems and Copper Tubes in Domestic Heating Systems. The same principles apply to plastic piping as well.[/quote]

Thanks some light bedtime reading tonight! I am starting to wonder wither I might be capable of sorting the emitter side of things myself cutting out the plumber and leaving the engineer to do the stuff with the Diakin kit.......

 

[Biggles..]

As usual agile has given his inexperienecd view of a heating solution.

If comparing ASHP to the other fuel choices you would actually arrive at the following,NG boiler manufacturers achieve a cop of 1,1KW in 1KW out,technically 100%eff.

Standard HFC ASHP when compared primarily running hotwater gives a cop of 1,radiator heating 1-2,UFH 2 plus.

In comparasion to other fuels the proven sustainability wouldlace place fuels in the following order (best to worst)
ASHP/GSHP-NG-OIL-LPG this takes into account,extraction,refining,transportation,installation,running etc.

At present it appears youve chosen a HFC type product,therefore your having to oversize the radiators to make up for the poor performance of the unit.What happens is the HFC's use a gas that at high temp doesnt perform(gas boils off) limiting the high temp to 50degc(ish) and at cold temps,less than 8degc also fails(gas condenses) causing the unit to run in permenant defrost.Considering most of the uk has sub 8degc winters,when you most need your heating HFC ASHP wont work.
To overcome this error,one manufacturer has introduced a high temp HFC,which is a cascade of two gases.The first gas warms up as normal then the second stage takes over giving a higher than 50degc temp.Problem is if its less than 8degc the first stage still fails and the second stage is useless.

If this is your chosen route,why not look at the stelrad K3,specifically designed for low temp supplies without having to lose valueable wall space.

At present the best solution for ASHP,is the Sanyo CO2 eco. A high pressure CO2 unit that acheives 65deg C circuit temp down to minus 15degc.What this means is no oversizing of radiators to the extent of other designs and a unit that doesnt need electric boosting to sanitise your hot water.

Im just in the process of installing a sanyo system based on our own design parameters for a client to use as an industry case study. The reason for chosing this product is simple,it works where all others dont.The others were only insatlled as originally they had all the MCS check points covered,since MCS and the grants have been scrapped,manufacturers are now taking note that the original HFC products dont match up.


forgot to mention,sanyo cop when combined with the dedicated acv tank in tank store.......3-4 for all uses.Thats 1kw in 3-4 out.


Lee

 

[Norcon]

It still doesn't add up Icgs no matter how good the cop is imo..
A 9kw model with matching thermal store is £8k + installation costs.
If I wanted to install one in my home it would fall short by at least 15kw.

So I fit two costing £16k and in the depths of winter I'm still cold.

These new technologies are great but at those costs they are not an option. Except for people with loads of money of course who want to prove their green credentials.
SHT from Austria have just developed a log/pellet boiler (TDA Thermodual)with automatic change over to the pellets once the log fuel is expended.
The 30kw model is nearly £12k.

 

[Biggles..]

Not sure where your prices are but your way out.plus you wouldn't need 2 stores.

As for pellet,just comparing a design at the minute where biomas would be my option, the reality is biomass is 2-3 the cost for material.have just this afternoon sat down with a comparison between a Hoval pellet burner,store,load levelling kit,calorifier,associated pumps and pipe.....it works out £15dearer than 3ashp units and tank plus there's no guarentee of getting the 10m3 pellet store through planning.

As for 30kw that would sugest using the industries crap guidelines you live in a 300 sqm pad(total floor area).my case study is in directvrelation to this I know from experience that if your house is insulated to the latest guidelines your heatloss at max should be between 35-50w/m2. This would see you living in a 600sqm palace.

 

[Biggles..]

Sorry bad maths you said 24kw-240sqm or 480 if utilising proper heatloss figures.

That's still one big pad.

 

[Agile]

As usual agile has given his inexperienecd view of a heating solution.



forgot to mention,sanyo cop when combined with the dedicated acv tank in tank store.......3-4 for all uses.Thats 1kw in 3-4 out.

Lee

Since I dont make personal comments about you then I dont see why you want to about me. Perhaps you take advantage of the fact I dont abuse people?

Nothing you have said disagrees with what I said.

Now that last comment. 1kW of electricity costs aroung 13p. For that you get 3-4 kW making a kW about 4p.

But NG now costs less than 4p so there is no cost advantage in using a heat pump if you have NG!

Since UK electricity is made from fossil fuels, using it to power a heat pump is not a sustainable fuel usage. Although a heat pump is better than using the electricity on its own.

Oil prices vary greatly but are perhaps about 4-5p per kW so the heat pump may have a small advantage. With LPG a slighly increased advantage.

But the main problem of heat pumps is a higher capital cost, a short warrantee and horror stories of bad failures. I met someone in France who had a lovely new house with a heat pump which packed up after three weeks. He then spent two years taking the firm to court and two years without heating!

Norcom, surely logs and wood pellets are both "solid fuel" ?

Tony

 

[Norcon]

Sorry should have said "once the logs are expended".

 

[Biggles..]

Fair point about the comment,but do you have any real life experience of sustainable products or is it just what you've googled.

Yes the Ecodan goes bang,but hey serves people right for fitting mitsi.

If you truely believe ng is the best thing available and cost effective, that's upto you.

The reality is I've just point my money where my mouth is,using norcons figure of £8k per say I've just agreed to fit ashp in a clients home at the cost I would have installed a shiney Vaillant boiler and aurostor.From that you can work out my contribution.watch this space I'll let you be one of the first to read the report and cost savings.

 

[Agile]

No, pellets are still a "solid" fuel even though they are smaller than logs.

They are solid as compared with a gas or liquid fuel.

The problem with pellets is that they are only cheap now because they utilise waste wood. If they used wood grown just for making pellets then they would be much more expensive.

Tony