Hello - first post and I am installing an ASHP

[bassman]

Always wanted to be batman

[JonG]

Apologies Bassman, too late and too many projects on the go! The offer still stands though even if you aren't quite as heroic as I might have suggested.

Just some more background on the jobs listed before, now I have some more time.

The Nordic is on a retrofit with an extension, a mix of UFH in screed and pug with tiles and oversized rads. We are expecting it to improve because about a third of the ground floor is yet to be insulated, some of the UFH has not been laid and some of the existing UFH is exposed.

The twin Daikins are on a new build with good insulation levels and UFH throughout in screed. The design of the UFH was not ideal though with a max temp of 43 degrees at minus 3, we design for 35 degrees with 100 mm centres and 80m max loop lengths. Floor coverings are tiles and carpet and although the customer swears blind they are less than 1.5 tog I am not convinced!

Both are into buffers and use sampling to control the buffer temp.

The NIBE should improve too, we discovered last week that the 3 port had failed and prior to this it had intermittently been failing during hot water production, spiking the floor temps and overheating the buffer. Valve is being changed out on Friday. This is a barn renovation with our own design of UFH in a screed with tile, but there are a few too many rugs in the main living area that I flagged to the customer last week.

Thanks for the link Sam I'll have a look at those, it looks like it fits in line on the return?

Jon

[sam123]

Thanks for the link Sam I'll have a look at those, it looks like it fits in line on the return?

Jon

Yep, return line. And probe to outgoing line.

0.6 model is suitable for radiator/UFH line. 1.5 model for GSHP ground loop or similar. 0.6 is about to 0.6m3=600 liters = 10 l/s flowing 

Sami

[Stochengberge]

Intresting reading...

I'm considering an ASHP to supplement the oil boiler, but without a Buffer Vessel. Am I wasting my time / money?

Boiler and DHWC are not two years old, and the DHWC is a triple coil affair, with solar in the bottom, oil on the top and soon to have a WBS in the middle. CH via radiators & 3.6kW PV on the roof so "free" electricity (until smart meters that double as Export meters spoil the party!!!). House is empty most weekdays, but I have a wife that feels the cold - I'm in shorts & T-shirts, she's in jumpers & fleeces!
The ASHP would only run if it's CoP was sufficiently high otherwise the oil boiler would cut in. I haven't got anywhere to put even a couple of hundred litre buffer vessel, so the ASHP would be directly feeding the CH - low grade heat to radiators.

So I'm wondering, if there is good sun for the PV to be working and run the ASHP for free (ish), the chances are the demand for heat won't be that high. Otherwise the CoP would have dropped off and the oil boiler will be utilised...


Hopefully you see my dilemma and some bright spark can put me right!


Through a work contact I can get a good deal on a Grant Aerona, but now concerned about what Jon G was alluding to:-

Grant is a long story only worth telling if someone is considering one.

Thanks.

[JonG]

SB, you need to think about the load first i.e. the heat loss, which is now very stringently controlled via the new standards and if you are going bivalent there has to be a common control strategy for the oil integration which does limit your choices to a degree in terms of unit and there are now also guidelines about how the bivalency is set up. e.g does the ASHP drop out at equilibrium point or is it supported by the oil boiler. If the latter you would need to consider a buffer to deal with defrost issues, to provide you with a "hot" reservoir if the energy in the house is low due to reduced setpoints because you are not there.

If you are thinking of having the heat pump cover marginal loads above around 6 degrees defrost is unlikely to be an issue so a buffer would not strictly be necessary for defrost. However you have to ensure that you get the flow rate for the unit and minimum system volume at all times, any zones, TRV's and so on could cause an issue as would 10mm circs. Make sure a flow meter is installed and delta t's are rigorously checked at commissioning. This would also affect your decision regarding the unit, for example Daikin's need a 5 degree delta T which is difficult to hit on rads, Mitsubishis work to a 10 degree delta but cannot be integrated into a bivalent strategy yet. Swedish units like NIBE and Danfoss are easy to bivalent but would require a buffer. We have creatively managed to accommodate buffers before, using out buildings, lofts, bespoke outside insulated enclosures etc.

You will also need to think about rad sizing to maximise efficiency from the HP. Also the cylinder does not have a separate coil for the HP so I am guessing it would be heat only, if not the coil needs to be sized to suit the low flow temp off the HP.

The Grant was commissioned and designed by them using various components from different manufacturers. It is a fixed speed unit which can have up to a max of 6 starts an hour which is huge variance from common thinking which generally targets no more than 3. This wear and efficiency issue cannot easily be resolved because the on off is dictated by a LV switch from a standard stat, as opposed to a thermistor which would usually be employed with a buffer. The programmer is restrictive in terms of user settings and manipulation for site specific conditions, including recruitment of the immersion and setting the bivalent point. We picked up an Aerona after it had been installed and left unfinished by the original installers. So far we have been unable to get the cylinder above 35 degrees, despite the fact it is a Grant designed HP cylinder with a solar coil that we have also used to try and increase the heat transfer.

Grant make very good oil boilers but the Aerona has some classic design faults that they openly admit were originally designed in to suit the UK market (no buffers), an inverter without a buffer can be problematic but a fixed speed ASHP without a buffer is not a good idea at all. Their cylinder routes the primary coil through the cylinder and back-up so that the return leaves at the same height as the flow, this has the effect of driving up the return temps as it accumulates heat from the hottest part of the cylinder and switches out the heat pump on the return sensor before the cylinder stat is satisfied. The base design is for an S-plan layout (2-2ports) but this is not a hot water priority set up so when the hot water valve energises the space heating valve stays open. the HP ramps flow temp and feeds the house and cylinder simultaneously, overheating the house and under heating the cylinder. Apparently this was because it was too complicated for plumbers to set up the required relays to shut the house valve when the hot water energises. Their solution is a packaged £200 relay switch to bring the cylinder immersion on at around 40 degrees to hit 60.

Hope this helps.

JG

[Stochengberge]

JG - thanks for the information (and the heads-up on the Aerona) although I would have to say I had to read it several times to try and understand!

Whether it is either / or for the heat source, I hadn't really considered. My initial thought was that as the CoP dropped off, the oil boiler would take over, but if they can be used in conjunction to get the most efficient solution, happy days.
Although you have now got me thinking, could you have a floating bivalent point? As the price of oil & electricity fluctuates, so will the preference as to which would be the less expensive heating option.

I think that you are saying that the ASHP needs to maintain a constant flow rate and that zones etc can upset the balance. As we have 18 rads over 2 zones, it strikes me we would be on a hiding to nothing as the volume is going to be variable. As an aside, the existing system is currently open vent, does this mater? If it is an issue, could the ASHP be integrated via an PHE? That way the systems are split, the ASHP can be pressurised as required and the volume of fluid in the ASHP circuit will be constant...

As for the radiator sizing issue, I was figuring that if the external temperature was high enough for the CoP of the ASHP to be acceptable, the heat demand would not be overly high and a slower rate of heating would be acceptable. Or is this naive?
I have to admit, I don't quite understand what you mean by

Daikin's need a 5 degree delta T which is difficult to hit on rads, Mitsubishi's work to a 10 degree delta...

It was my intention to leave the DHW running off the solar / WBS / oil boiler as ASHP's struggle to heat to 60'.

From what you appear to be saying about the Aerona, what I save on the unit, I will loose out on performance.

Thanks for taking the time to reply, and hopefully I have understood what you are saying.

 

[JonG]

As far as I know the only product that calculates the fluctuation in utility prices and chooses the best option based on user inputs, is the Gloworm heat pump and hydrobox module. This would be worth a look in your particular instance, we actually helped with some of the design parameters on this product but have to confess to never actually having fitted one becuase we tend to always aim for 100% coverage from the HP to ensure any RHI is payable, but when we saw the pre-production mock ups it did look good and very clever in the way that it selected the most appropriate heat source for the property at any given set of parameters. It did also have the HE you refer to to match it with an existing system, but from memory both sides have to be pressurised. If you make contact with your local Gloworm rep via a merchant I am sure they will provide more information on it.

Where are you geographically by the way?

The zone and flow rate aspect was another reason why we were shy of the Gloworm product, 18 rads and 2 zones is fine, it is multiple floor zones that cause the most headaches, where each room is a separate zone. We always use a buffer to guarantee flow rate and provide for defrost, which mitigates to an extent, what is downstream anyway.

In terms of the radiators, because the unit should weather compensate, whilst the demand is lower at higher outdoor ambients, the flow temp will reduce and therefore larger emitters are still needed. If you really can't or don't want to upsize the rads a high temp may be worth looking at, but price and complexity increase and efficiency decreases.

The delta T is the difference in temperature, in this case between flow and return. the heat exchanger in each heat pump is designed with different optimal performance levels based on flow rate and delta T which are a function of each other. This is another reason why we use buffers and something to consider if you end up using a PHE, due to the need to match its performance with that of the heat pump in terms of heat transfer, flow rate and delta t.

In terms of hot water, we tend to always target around 48 degrees store temp to avoid daily immersion usage and then pasteurise periodically. This is usually within the capacity of most units.

The overriding point about heat pump systems is that simplest is best, bivalent can work but you will need to source a good installer to get the best set-up and ensure that the HP is designed to be easily integrated and controlled.

If you can make a stab at your heat loss and provide some insight to your insulation levels I might be able to be more accurate about HP specifics.

 

[desperate]

Thanks for your informative posts JonG, I too have an HP idea bubbling away at the back of my brain, may start a new thread soon.

Desp

[Stochengberge]

JG -thanks again.

The Glowworm looks like a possible solution, but it does seem to imply that the heating circuit would need to be pressurised. I will follow that one up.

You imply that the RHI (if they get it sorted) is only likely to be payable on stand alone systems. A bivalent system would not qualify. Am I reading this right?

Some of the rads will need changing in the not too distant, but wasn't planning on doing them all in one go. According to the Myson website, they would need upgrading by a factor of 2.4. When you consider that we have 18 of them, and most are 1600mm twin panels, that won't be cheap! That and the fact that we aren't going to have a lot of wall space left!!! I would love to go underfloor, but that is another expense we can't stretch too.

The property is in the Maidstone / Sittingbourne area of Kent. Cavity wall insulation was done last year and we have masses of loft insulation. 217m2 of floor space with a Grant Oil boiler rated at 19kw. Double glazed throughout, but they haven't got the best U rating in the world. Solar Thermal & PV already on the roof. Built in 1972 by the church, to a good standard. (Square, straight walls, solidly done.)

Thanks for the explanation on delta T. I was guessing that is what you meant, but thanks for confirming it.

I have also been reading the EST Heat Pump Field Trial, which basically says that the success of an installation is primarily down to the way it is installed and the commissioning. It also says that you should keep it simple, which it seems to me I am endeavouring to do anything but!

It does seem that I have managed to hi-jack someone elses post. Being a Newbie, if this is bad form, perhaps one of the Moderators could let me know and I will start a new one.

[JonG]

No problem at all. We are in the NW so can't help physically I am afraid. If you have a look at this link http://www.microgenerationcertification.org/installers/installers/decc-heat-pump-training-road-show there is a raft of information on sizing and on the right hand side a Heat Emitter Guide that you can use to ascertain whether the existing radiators would:

a. Work with a heat pump without up-sizing albeit at a lower COP
b. Confirm up-sizing factors and impact on COP

We use K3 rads quite a lot now which are triple panel triple convector, so footprint is smaller but depth greater.

At 217sqm and the insulation values you describe heat loss would be in the region of 11kw very roughly. This should be coverable on a Daikin Altherma LT or Nordic or a Danfoss DHP-AQ, both can be set up for bivalency. Not sure what the outputs are on the Gloworms.

One of the best references I have on the subject is John Cantor's book which is a worthwhile investment if you are serious about the project. http://www.heatpumps.co.uk/

In terms of the RHI, basically who knows! We have always worked on the premise that it will not permit bivalent operation, despite the fact that it makes excellent sense in some instances, also the latest MCS guidelines cover bivalency in some depth so maybe they are relenting to a degree. I know Gloworm were petitioning hard to justify their R&D spend.

Some of the Grants can be pressurised or open vented, depending on when they were manufactured, be worth a call to them to check.

Happy to help if I can Desp.

Cheers

JG