Private district heating

tim smith

I think encumbering properties this way might bite you in the future unless you know these properties will continue as one enclave. I like the idea of district heat but only if it was a planned community or such or condo/townhome community. Tim

Bob Vennerbeck

Private district heating

By various accidents of fate, probate and the economy we have assembled a handful of residential rental properties adjacent to our home in Providence, and would like to start brainstorming about the possibility, benefits and pitfalls of moving towards a private 'district heating' system, with a geothermal source. Those are two large and unusual concepts (at least for us as midscale landlords) and we are particularly curious if they might work very well together, or should be considered separately on their individual merits.

Thanks for any thoughts, references, or pointers!

Vbob

Perry_5

All studies I have seen agree on several points

District heating (& cooling) is a really great concept - that almost never gets implemented as a new project due to one thing: Initial construction cost.

The secondary concern is the cost of long term maintenance (for when the pipes leak). You have to be ready - and have the funding for - Digging up the street or the yard (or have a more costly initial construction with tunnels and conduits).

The third consideration: establishing the required covenants on the buildings to cover when ownership transfers. Such projects do not work if new owners decide that - afterall - they can heat cheaper with wood or something and want to go off on their own.

As a combined geothermal project... Tougher yet; and you really have to be careful to ensure the collector field is really properly sized (actually - properly oversized to cover bad years).

So lets look at the concept:

I've read a number of studies on community size projects and here are the key points on large scale projects:

First off: If you are going to build heating - also building distric cooling can be done at the same time; and it greatly enhances the economics of the project. Domestic Hot water is also heated by the system.

All the houses will need to be heatable and coolable by the same technologies: Classically this has been steam and chilled water. New steam systems are rarely built now unless you really have a large project and most new district heating is centered around hot water. However, new industrial, educational, hospital, etc complexes are still built with district steam heat as steam is the most efficient due to the elimination of pumping cost.

To minimize pumping cost on the hot water you need large pipes.

Hot water and chilled water piping needs to be appropriately buried and insulated in a manner that can be accessed for repair in 20 - 30 - 50 years without degradation and damage. Several studies I have seen indicate that use of prefab concrete (or composite) trench vaults would work (typically 18-36" wide, x 18" deep, with lids). The pipe with insulation (lots of insulation - and resistant to long term aging and water breakdown) is laid in these trench vaults and packed in sand; and then the lid placed on the box - and then buried (with diggers warning tape strategically placed above the trench boxes).

An alternate strategy that I like for entire communities that can be done with new construction is the concept of Utility tunnels under the streets. Then well insulated conduit is run to each house and flexible piping materials used for the hot/chilled water supply and return piping pulled through the conduit. Other conduit handles electric, water, phone, cable, etc. The key advantage is that all utilities runs to the house can be replaced or upgraded without digging up the yard and street. Very expensive to build - but very good long term advantages (> 30 years). Requires cooperation of all utility companies. No one has built this in the US in at least 40 years due to initial construction cost - although all studies indicate that on a 50+ year timetable that this is the most economical for a new community.

Direct burial of individual insulated lines without using a vault or heavy conduit may be cheaper up front; but has been found to have a lot more long term issues with degradation of piping, insulation, and damage - requiring more frequent digging in streets and yards after a decade or so.

Individual house metering systems need to be inplace for both the hot and chilled water, with a billing structure to pay for all initial construction cost, fuel cost, current maintenance, and future major maintenance.

You need to establish a trust type fund for emergency major repairs to leaking underground piping; otherwise you jeopardize the entire system - and all buildings - from a single leak. It is wise to also charge enough to slowly build up system replacement funding.

The heating and cooling plant is build with a robust redundant design. Multiple boilers ganged together to provide both highly efficient operation and also reliability as a boiler can be down and the system can still operate efficiently. Multiple chillers, multiple pumps, etc.

Having the all supply and return piping on a loop with periodic mid loop isolation valves also allows you to supply and return from either end of the loop while repairs are being done on a middle section.

Unfortunately, despite the overall efficiency and long term economics of such a system - Initial cost and politics have prevented the construction of such a system in the US for many decades.

I do note that part of this has been applied to a solar heated community where people were willing to pay a premium for their new houses and to live in the community. This uses geothermal storage - and I think you will be interested in the concept:

http://www.dlsc.ca/

Do a search on "Drake Landing" and you will find severarl articles as well.

So much for a community wide system - how does it relate to your concept:

While it may seem simple to just have one (or 2) large boiler in one house - and pipe the water to and fro; and you could maintain them yourselves.... and while you may be able to make a short term economic case for that for a few years.... You need to also think of the future. Who is going to run and maintain this tomorrow if you get smucked by a meteorite. What happens if the houses are sold off one by one. How does it work. What happens if you have a fire in your boiler room (or in the house with the boilers). What happens if one of the buried pipes leaks. Do you have the resources now (and in the future) to do an unscheduled dig up & repair or replace a pipe in the worst cold weather through frozen ground.

The reason the most district heating systems have died in the US was that the district heating utility was not funded sufficient for emergent and future repairs and replacements.

The fact is that unless you have a robustly constructed redundant system with proper maintenance and funding for the future (which is the expensive way to do things) - that individual utilities and individual house heating and cooling was more reliable.

I never understood why the US did not develop district heating & cooling utilities - regulated by the state utility commission - similar to electric, gas, and water utilities. That would seem to offer some solutions to the issue.

I'm not sure I directly answered your question. But I do hope I gave you some things to think about.

Perry

Bob Vennerbeck

thanks for thoughtful responses

Perry, Tim - thanks for good points to ponder, especially on long term maintenance and single points of failure. We have access to skills and heavy equipment on a barter basis, and large amounts of enthusiasm in our (small) community. The houses are at most 50' apart, so the added infrastructure is not as terrifying as it might be, and we already are in the habit of overdoing our upgrades...
I understand full well that we might create a complex legacy for the next generation, but we have this community largely because the last few owners had little or no thought for what might happen to their property after them, and we are thinking of doing things differently, not just better.

Very much in the blue sky stage, but we want to get our brains warmed up while the ground is too frozen to let us get ahead of ourselves.....

Thanks

Vbob