Central Heating - Sealed OR Open Vented Systems?

[andy-houghton]

I have recently purchased a small corner shop which is attached to a semi-detached house.

The shop was originally used for selling antiques and did not have water or gas laid, neither did it have a toilet, but that is being taken care of during its conversion to a small video studio for my business.

The house side is converted into 5 small one bedroom flats and these are all electric for both heating and hot water.

I am going to be putting Gas Central Heating into the shop and eventually all of the flats but this will only be done as each flat becomes vacant both for cost reasons and also to not inconvenience the current residents.

I have just purchased a Gloworm 38HXi Boiler which should more than handle the heating requirement - eventually for the whole building, I have already started work on piping both the shop area and one of the flats which is currently vacant and I am now looking to install the boiler.

There is still time to change the system to suit either - A Sealed System OR an Open Vented System with an expansion tank in the loft area. This Go-worm boiler does support a sealed system if required with the addition of an expansion vessel, pressure guage and safety valve etc.

Obviously if I opted for the Sealed System I would need to calculate to Expansion Vessel but what size of vessel should I buy i.e. One that is big enough calculated for the whole flats or just for the current shop and one flat? If I opted for the larger vessel, would this still work only heating two flats at this time? Or would I have to change the vessel each and every time I expanded the system into the rest of the flats?

What would you do? Install a Sealed System OR Vented System? the latter I would presume would cause less of a headache or am I getting this wrong?

Please advise.

Andy Blackpool UK

[John Rumm]

Out of curiosity, how will you be metering the energy consumption of each flat? or are you just planning on charging a flat rate?

Fit a vessel large enough for the final system now, and you will be fine. There is no problem with "too much" expansion volume - only too little.

Sealed certainly. Especially if there is a possibility a flat may be empty and hence a leak could go undetected for a while.

[David Hansen]

On 4 Feb 2007 05:32:12 -0800 someone who may be [e-mail] wrote this:-

Install an open vented system. More tolerant of abuse.

[Roger Mills]

Go for a sealed system - you will then have virtually all the critical bits under your direct control in the shop, and won't need to go into the flats to attend to things.

Go for an expansion vessel big enough for *all* the flats. Having too much expansion capacity is never a problem - it just means there is less pressure rise when the system gets hot. Having too little capacity *is* a problem.

Design it as an S+ Plan system from the outset - with a separate zone for each flat. It is then simple to expand flat by flat - just adding a zone valve and programmable thermostat each time.

As John has suggested, you need to think about how you will charge the flat occupants for energy consumed. [I'm sure whether his reference to a 'flat' rate was an intentional pun - but I fell about!]

[andynwuk]

Charging for central heating for each flat can be a problem unless the occupier has an individual Gas Meter which in this case they don't.

I have asked around other Flat owners in Blackpool and they normally charge a "Flat Fee" per week.

However, I am a qulaified Electrical & Electronics engineer and my idea was to purchase card meters to install into each flat that will control the Zone Valves for each flat repectively.

Using this method and with careful calculation to ensure I am not overcharging the tennant or of course losing out, I would base the card readers on an hoursly consumption. I can charge the number of hours onto the chip of the card with pre-payment from the tenant.

Each Tenant woul have their own programer which simply controls the Zone valve to their flat, once the card reader detects the programer is calling for heat, the time strats to count down until the heating call is cancelled either manually or by the programer time.

The card meters I have looked at can also accept coins in an emergency and are fully programable for both formats.

Andy

[adder1969]

Surely he's going to charge them all a high rate then only have the heating on for an hour a day ;-)

Seriously, I'm not sure if there's anything to worry about with it being two properties but the heat to one supplied from the other, with it would seem the gas supply actually coming from the house side.

[andynwuk]

Hi Roger,

Thanks for you reply, like I explained to John earlier, I am intending to supply each flat via an individual Zone Valve as you reccommended. However, instead of a wall stat, I thought of using Thermostatic Radiator Valves.

The flats consist of a small lounge, 1 x bedroom, kitchen and shower area/toilet.

I calculate three radiators would surfice in each flat i.e. Lounge/ Bedroom/Shower Room.

Obviously using thermostatic valves, I would most certainly require a bypass pipe adding to the system which I will do.

I will have a Corgi Registerred engineer to connect the Gas side and certify the installation on completion which goes without saying, I just want to get this right the first time around being a typical engineer and expert advice from your side is very much appreciated.

Many thanks again.

Andy

[David Hansen]

On 4 Feb 2007 06:53:56 -0800 someone who may be [e-mail] wrote this:-

Do what they do in places where charging for heat supplied is normal. Measure the flow and temperature and this indicates how much heat has been used in a particular dwelling. It may even be a standard feature of some controllers.

[David Hansen]

On Sun, 4 Feb 2007 14:34:16 -0000 someone who may be "Roger Mills" wrote this:-

Other then the F&E tank being in the loft, how is this different to an open vented system? Is the loft part of a top flat?

Is there any difference between both systems in this respect?

[John Rumm]

In truth, I missed that until you pointed it out! ;-)

[Stuart B]

You could describe it as 6 properties .could you not .

Using TRV's does that mean that they will never be completely "off" even when turned down to the lowest position ?....assuming they have a "frost" position so the tenants have limited control over them and no access to the boiler control .

What will be the hot water situation when all the flats are converted to CH .Will the system be able to cope with 5 flats and a shop needing hot water .?

[John Rumm]

In which case you come back to the usual problem of not having any from of interlock to stop the boiler firing when all the heating demands are met.

Personally I would fit a programmable stat to each flat, which would control each zone valve via your card meter. Set the meter to only charge when there is a demand from the stat. Each zone valve could be wire or'ed to call for heat from the boiler, possibly via a master programmer under your control (so if you decide that you don't want the boiler running between 1 and 5 am say then you can enforce that)

Another advantage of a stat based control in each flat would be less demand on the bypass (although you will need one master one somewhere to allow pump overrun when all zones are satisfied). You also are more accurately charging for the heat used since otherwise the flats programmer could be demanding heat all day (and charging) but the TRVs be mostly shut. Given the large number of zones, a modulating pump may be a good idea cope with the range of flow resistances that it will likely meet. In this circumstance it may be worth having the bypass zoned as well and only enabled when all zones are satisfied - this could save it passing water at times when not required and lowering the boiler efficiency (by raising the return temperature).

How are you proposing to provide hot water for the flats? Making each flat a C plan system in its own right would probably work ok if they each have cylinders.

If you are trying to avoid engineers, you have probably come to the wrong place! ;-)

[andynwuk]

Hi Stuart,

The Flats are technically classed as "A House of Multiple Occupation" according to Blackpool Borough Council which is good as there is only one "Council Tax" to pay. One of the Flats is a Bedsit and has a separate toilet for that tenants use down the hall on the landing area, so because all the flats are technically classed as not being "Self Contained" the building remains a converted house and as they say "A Home of Multiple Occupation".

The Hot water question, the flats currently run everything on electric including using Sadia Water Heaters in the kitchen areas and Hand Wash units in the bathroom wash basins, the showers are all electric also.

It is very difficult to charge for the individual water usage apart from the way it is at present i.e. heated by electric as each flat does have its own electricity meter installed. which are sub meters off the main one belonging to the Electricity Supplier. The electric bills when adding all the meters up actually are very accurate in meeting the same figures of that shown on the Electricity Boards meter. So no problems there.

Andy

[andynwuk]

Hi again Stuart,

Sorry forgot to mention in my last posting - Yes the Tenants will have a programmer installed to control the Zone Valve supplying their flat. Don't forget that if the programmer is calling for heat - then the Tenant will be paying for it as the hourly units will be counting down off their card as previously mentioned in an earlier posting, so in fact they will be paying for it!

This is a fair system as if you have a Tenant that goes out to work for the day - they can switch off their heating system. On the other hand, a retired Tennant for example may want to have heat on all the time which makes the system flexible.

The Zone Valves will control the Boiler and Pump, if all programmers from each flat are set to off, then all the zone valves will be closed and this will in turn turn off the boiler and pump.

Best Regards,

Andy

[<me9]

It is possible to get meters to record KWH of heat consumed.They have a flow meter and a pair of temperature sensors. We used them at work a few years ago (for a different purpose) but they are designed for metering in district heating systems.

I don't know the cost (certainly more than an electricity meter) but they were of scandanavian manufacture, where district heating is more popular.

[Stuart B]

Ah.It's a HOMO property then ..LOL

[andynwuk]

Are you suggesting I can get some kind of in-line Water Flow Meter to put in after the Zone Valve to the feed of each flat that can monitor the flow more accurately? Then simply find another instrument to measure the average temperature?

The method I thought of to calculate the heat output was to work out the Kwatt hours of the radiators in each flat (as some flats are larger than others - opne being a bedsit for example) and the number of hours used in each flat which can easily be obtained from the smart card and do a maximum calculation. After the first couple of heavy quarters of gas usage, I should be able to obtain a rough cost per hour from each flat. I know the rads will be switching in and out and this is why the study will have to be done over a period. However, if you could enlighten me more on the flow v temperature method and what is used to measure this then this may be an even better method for me to use and more accurate.

Best Regards,

Andy

[Ian Stirling]

Unfairnesses: If the boiler does not maintain a constant output temperature, then simultaneous users will be overcharged as the heat output drops.

If the boiler does not maintain a constant - and identical - pressure to each flat, then users that use heat at unusual times will get it cheaper.

TRVs on each rad will mean that someone that turns the TRVs down on all but one rad will get quite expensive heat from that rad.

The cheapest way I can think round this is to place bypass valves, set to a low pressure differential at each flats flow and return, so that it is set to around the same pressure differential as the 'full open' loop resistance of the pipe.

So that the pressure into each flat stays the same, and you don't get cross-coupling between flats, assuming the boiler stays at maximum output temp with varying loads.

Then inform them that they get the price assumes that all the TRVs are open, and the thermostat is what is being used.

[David Hansen]

On 4 Feb 2007 08:02:34 -0800 someone who may be [e-mail] wrote this:-

No. I know that you can.

There are plenty of such instruments. One in the flow and one in the return gives the temperature difference.

Standard way of measuring heat supplied, any one of the standard reference works should describe it.

"Measuring instruments" section and "Calorimeter module WMZ-M1".

[Roger Mills]

Don't know for sure, of course, but I assumed it probably was.

Again I'm assuming(!) that the OP will be based in the shop and that the boiler etc. will be there. Having the pressure vessel and - particularly - pressure gauge all in one place means that he can see at a glance that everything is ok. F&E tanks in attics tend to dry up when their ball valves seize - and can go undetected for a long time.

Also, with the vast range of flow demand to which this system will be subjected, the potential for pumping over in a vented system is considerable.